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One of the best things about baseball is that ballplayers can stick around for a long time if they're good enough. It's not like football, where even the best players will be lucky if they're still worth a darn at the age of 30.

But there comes a time when even the best ballplayers must hang up their spikes. It's just a matter of knowing when the time is right.

The question is: How can they know when the time is right? Is there any sort of checklist for superstar players to consult before making their decisions final?

Sure there is, and it's not very complicated. Or long, for that matter. Which is good, because long and complicated things are fun for nobody except accountants and cartographers (I'm not sure either, but just go with it).

There are obviously different checklists for pitchers and hitters. This week, I'm presenting the checklist for hitters. If you'll follow me this way...

The Primary Test Subjects

Like any sort of experiment, this one requires a sample size. In this case, a study of superstar hitters requires an appropriate collection of superstar hitters (no J.D. Drews or Jason Kendalls allowed).

To ensure the study is relevant to this day and age, in which ballplayers can stay healthy and productive for longer due to advancements in medicine and training methods, a sample of strictly contemporary ballplayers is an absolute must. To this end, we'll go back to, say, 1985?

And we'll pick out our sample size using—what else?—WAR as a guideline. By Baseball-Reference.com's reckoning, here are the top 15 players who have come and gone (an important part, that) in Major League Baseball (another important part) since 1985:

Barry Bonds: 158.1 Chipper Jones: 81.5 Ken Griffey Jr. 79.2 Jeff Bagwell : 76.7 Rickey Henderson: 73.5 Wade Boggs : 70.8 Frank Thomas: 69.7 Larry Walker: 69.7 Cap Ripken: 69.2 Barry Larkin : 67.1 Rafael Palmeiro : 66.1 Kenny Lofton: 64.9 Manny Ramirez : 64.8 Edgar Martinez: 64.4 Ivan Rodriguez: 63.7

We'll look at a few more notables along the way, but this 15-player sample size offers just the right amount of diversity. It includes average guys, power guys, speedy guys, defensive wizards, defensive liabilities and, of course, a couple players with strong links to PEDs.

I went and looked at each of these 15 guys individually and came up with a rough idea of when they were in their primes and when they were in their twilight years. No real exact science went into determining what was what, but primes generally started when these players first established themselves as stars and ended when their numbers started to slip.

It's why their numbers started to slip that interested me. It's like none of these guys could buy a hit towards the end.

Sure enough...

Can't Buy a Hit?

There's a lot more to hitting than simply putting the bat on the ball. It also entails things like walks and strikeouts, which make for a huge part of the overall act of hitting.

Among our 15 players, I didn't see any discernible patterns in terms of walk and strikeout rates between prime years and twilight years. They're all over the place, which I take to be the result of several different factors (eyesight, physical skills, league pitching, etc.) all clashing together.

But what really counts here are the moments when the bat met the ball and results followed. That's how these guys became superstars, and it's also how they un-became superstars in their old age. When they made contact, the results just weren't the same.

That's a reality that their BABIPs (Batting Average on Balls in Play if you're just now joining us) can reveal.

Player Prime Years Prime BABIP Twilight Years Twilight BABIP Difference Barry Bonds 1986-2004 .287 2005-2007 .250 -37 Chipper Jones 1995-2008 .318 2009-2012 .291 -27 Ken Griffey 1989-2007 .292 2008-2010 .245 -47 Jeff Bagwell 1991-2003 .318 2004-2005 .296 -22 Rickey Henderson 1980-1999 .309 2000-2003 .270 -39 Wade Boggs 1982-1995 .349 1996-1999 .317 -32 Frank Thomas 1991-2003 .309 2004-2008 .268 -41 Larry Walker 1990-2002 .334 2003-2005 .321 -13 Cal Ripken 1982-1996 .277 1997-2001 .277 0 Barry Larkin 1988-2000 .314 2001-2004 .288 -26 Rafael Palmeiro 1988-2002 .290 2003-2005 .247 -43 Kenny Lofton 1992-2003 .327 2004-2007 .327 0 Manny Ramirez 1994-2008 .340 2009-2011 .332 -8 Edgar Martinez 1990-2001 .342 2002-2004 .312 -30 Ivan Rodriguez 1992-2006 .325 2007-2011 .309 -16

Out of these 15 guys, the only two who didn't experience a decline in BABIP in their twilight years were Cal Ripken and Kenny Lofton.

Their cases, however, are slightly misleading. I put the cutoff for Ripken's prime at 1996 because four of his last five seasons were mediocre by his usual standards, but the one good one saw him rack up a .340 batting average and a .952 OPS in 86 games in 1999, pretty good production for a 38-year-old.

A .332 BABIP had much to do with Ripken's success that year. Even for him, it was a high mark. The second-highest of his carer, in fact. And sure enough, it wasn't sustainable, as his BABIP in his last two seasons in 2000 and 2001 was a combined .245.

Lofton also benefited from an outlier BABIP towards the end of his career with a .373 BABIP in 2005. Among players with at least 400 plate appearances, that was the highest in baseball that year (see FanGraphs).

The season before in 2004, Lofton's BABIP was .292. In the two years after in 2006 and 2007, his BABIP amounted to .320.

If these two big outlier seasons are removed from the equation, the top retired superstars since 1985 just couldn't quite find the holes in the defense like they used to. That can be due a big heaping pile of bad luck in a single season, but over several seasons the more rational explanations have to do with the hitter himself. Declining bat speed, for example.

For the sake of being a little more thorough, here's a look at a couple more guys immediately behind our 15 guys on the WAR list since 1985.

Player Prime Years Prime BABIP Twilight Years Twilight BABIP Difference Roberto Alomar 1988-2001 .326 2002-2004 .293 -33 Craig Biggio 1989-2004 .318 2005-2007 .275 -43 Andruw Jones 1997-2007 .280 2008-2012 .236 -44 Tony Gwynn 1984-1997 .346 1998-2001 .319 -27 Mike Piazza 1993-2003 .323 2004-2007 .285 -38

Same thing, and I skipped over a couple guys to make sure Tony Gwynn and Mike Piazza were on display here. Per FanGraphs, they were the top two hitters of the 1990s in terms of batting average, yet they too couldn't get as many hits to fall when they got into their twilight years.

You may be sitting there thinking that this is a numerical evaluation of something that's common knowledge: Old guys just can't hit like they used to.

That's exactly what this is, and the obviousness of it is why this is the first item on the checklist. When star hitters get old and start seeing fewer and fewer balls off their bats find holes, they have to square themselves with the fact that they're not getting cheated. Baseball nature is taking its course.

To boot, it's not just getting hits when they put the ball in play that aging stars need to keep an eye on. They also need to keep an eye on their ability to hit the ball with some authority.

Or lack thereof, more to the point.

Can't Put a Hurtin' on the Ball?

Putting the bat on the ball and ending up with a hit doesn't always require hard contact. Bloopers that fall into no man's land and seeing-eye singles up the middle are just as good as screaming line drives right back at the pitcher's soul-windows.

But plays such as those never made anyone a superstar. Even guys who are stars because of their speed and/or ability to hit for average also show off a little extra-base power now and again.

Naturally, extra-base power is another thing that goes with age. That's something that ISO—or Isolated Power, which is essentially a slugging percentage without singles factored in—can reveal.

Here's our 15 guys.

Player Prime Years Prime ISO Twilight Years Twilight ISO Difference Barry Bonds 1986-2004 .311 2005-2007 .287 -24 Chipper Jones 1995-2008 .238 2009-2012 .174 -64 Ken Griffey 1989-2007 .264 2008-2010 .168 -96 Jeff Bagwell 1991-2003 .249 2004-2005 .189 -60 Rickey Henderson 1980-1999 .147 2000-2003 .102 -45 Wade Boggs 1982-1995 .119 1996-1999 .095 -24 Frank Thomas 1991-2003 .260 2004-2008 .238 -22 Larry Walker 1990-2002 .260 2003-2005 .223 -37 Cal Ripken 1982-1996 .178 1997-2001 .151 -27 Barry Larkin 1988-2000 .158 2001-2004 .119 -39 Rafael Palmeiro 1988-2002 .229 2003-2005 .205 -24 Kenny Lofton 1992-2003 .129 2004-2007 .106 -23 Manny Ramirez 1994-2008 .280 2009-2011 .202 -78 Edgar Martinez 1990-2001 .216 2002-2004 .171 -45 Ivan Rodriguez 1992-2006 .183 2007-2011 .119 -64

Not all of these guys were elite power hitters, to be sure. Rickey Henderson, Wade Boggs, Barry Larkin, Kenny Lofton and Ivan Rodriguez, in particular, stand out as players who will never be ranked among the elite sluggers of the game.

But even they suffered from power outages in their later years, albeit for different reasons. Henderson hit only 19 homers in his final four seasons, and only seven doubles in his last two. Boggs hit only 15 homers in his final four seasons. Larkin totaled 19 homers and 80 doubles in his final four seasons. And so on.

Beyond these guys, you'll notice that the sluggers stopped slugging at their usual rate as well. It wasn't just them, as these other noteworthy sluggers also stopped slugging in their old age.

Player Prime Years Prime ISO Twilight Years Twilight ISO Difference Sammy Sosa 1990-2004 .271 2005, 2007 .187 -84 Gary Sheffield 1992-2005 .248 2006-2009 .180 -68 Fred McGriff 1987-2001 .227 2002-2004 .205 -22 Carlos Delgado 1996-2006 .279 2007-2009 .220 -59 Vladimir Guerrero 1998-2008 .256 2009-2011 .163 -93

Between the sluggers in this table and the sluggers in the first table, the total collection of those who hit the ball hard for a living features a mix of both guys linked to PEDs (Bonds, Palmeiro, Ramirez, Sosa) and guys not linked to PEDs (Griffey, Thomas, Martinez, McGriff).

That all of them saw their ability to hit for power diminish as they got towards the end goes to show that, no matter what a hitter puts into his body, power is not infinite. It is, in fact, quite finite.

So when your power goes, sluggers, there's no point fighting it. Odds are it's not coming back.

As for you speedy guys, that goes for your speed as well.

Speedy Guys, Can You Still Run?

Here's where we have to deviate from the path a little bit and focus on certain members of our core 15 (others will join the mix shortly). For while most guys are going to achieve superstar status by putting the bat on the ball, others are going to achieve it or augment it with their legs.

These guys also need to know when to hang it up, and they'll know it's time to do so when, shoot, their legs just aren't the weapons that they used to be.

Take Barry Bonds. He's the only player in history with at least 500 home runs and 500 stolen bases to his name, but he didn't do much to pad his stolen base totals after swiping 13 bags in 2001.

Between 2002 and 2007, Bonds attempted only 33 steals in over 1,200 opportunities. In his last two years in 2006 and 2007, he attempted only eight in 368 opportunities. He was successful with these steal attempts, to be sure, but that doesn't mean he was a successful baserunner.

FanGraphs keeps track of "Base running runs above average," which is basically just what it sounds like. It's a stat that tracks how much value players provide on the bases, measured in runs above or below zero.

Between 2002 and 2007, Bonds amassed a BsR of -12.1, technically making him a liability when he was on the bases in those years. He wanted to become a slugger later in his career, and that's exactly what he became.

Among the speedy guys in our core 15, Bonds isn't the only guy whose legs didn't have much juice late in his career.

Rickey Henderson, baseball's all-time greatest base stealer, was caught stealing 32 times in 130 tries between 1999 and 2001 and basically stopped trying after that. He saw 148 stolen base opportunities in the final two years of his career, and attempted only 13 steals. To boot, BsR shows he ceased being an elite baserunning threat in 1998.

Ken Griffey Jr. basically stopped stealing bases when he joined the Cincinnati Reds in 2000, and his BsR totals reveal that he became a base clogger starting in 2004. He was out of gas.

Jeff Bagwell is one of the best baserunning first basemen in the history of baseball, but he ceased to be a big stolen base threat after 1999, swiping 44 bags with a 69 percent success rate. His BsR totals were hit-or-miss after then as well.

Larry Walker, another underrated stolen base threat, had a 78 percent success rate between 1990 and 1997. From 1998 on, he was successful only 70 percent of the time and attempted only 93 steals in over 1,700 opportunities. His BsR totals got to be all over the map.

Barry Larkin gave up trying to be a weapon on the basepaths after 1999, attempting only 46 steals in over 800 opportunities. He was successful 74 percent of the time he did try to steal, compared to 84 percent up until 1999. After '99, he had a couple good BsR years, and a couple not-so-good ones.

Kenny Lofton stole 77 bags with an 84 percent success rate in his final three seasons, not bad for a guy his age. However, despite stealing 23 bags in his final season in 2007, Lofton still barely qualified as an above-average baserunner in the eyes of BsR.

And on the narrative goes, spreading from members of our principle cast to the extras standing around to be called when needed. Here they are now.

Roberto Alomar stole at least 30 bases three years in a row between 1999 and 2001, and then stole only 28 in his final three seasons with lackluster BsR totals. Craig Biggio attempted only 88 steals in the final 2,213 opportunities he saw and rated as a below-average baserunner in his final two seasons in the eyes of BsR. Vladimir Guerrero attempted only 29 steals in the last 971 opportunities he faced and rated as a huge liability on the bases in his final two seasons in the eyes of BsR.

These narratives go to show that speed is at least as finite as power, and there's not much that can be done to combat the diminishing effect of age. Even those who scaled back on their running by limiting their stolen base attempts (Bonds, Henderson, Griffey, Larkin, et al) still found their skills on the basepaths to be lacking in their twilight years.

So old guys can't hit, they can't hit for power and they can't run. At least they can still field their positions, right?

Um, no.

Lost Your Position? Can't Play Defense?

If hitters see their bats and their speed go in old age, the writing will be on the wall.

The writing on the wall will be even bolder and in even bigger letters once it becomes clear they're either a) not wanted at their usual positions or b) no longer capable of fielding their positions the way they used to.

Among our core 15, there are only a couple exceptions.

Edgar Martinez and Frank Thomas had been everyday designated hitters for years by the time they retired. Big Hurt was still playing a fair amount of first base in 1999 and 2000, but those years were a distant memory by the time he hung up his spikes in 2008.

Then you have guys like Manny Ramirez. He was set to be the Tampa Bay Rays' regular DH in 2011 before he abruptly retired, but he was never great in the field to begin with. In fact, FanGraphs has him pegged as the worst defensive left fielder in history, a notion that my memories of Manny in the field (shudders) confirm to be plausible.

But then you have guys like Ken Griffey Jr., whose tale of woe still makes me cry out "Alas!" even when (or especially when) I'm in a crowded room.

Griffey was one of the best the game had ever seen in center field in his prime, but by 2004 he was consistently rating as a horrid defensive center fielder in the eyes of advanced metrics like Ultimate Zone Rating and Defensive Runs Saved. The Reds moved him to right field in 2007, and he was a DH not long after.

Cal Ripken, of course, was the subject of one of the more famous position changes in baseball history, moving from shortstop to third base in 1997. The defensive metrics say he wasn't so great at the hot corner after spending much of his career as a very good defensive shortstop.

Chipper Jones was displaced to left field in the early 2000s before eventually finding his way back to third base for the remainder of his career. The metrics say he was at best mediocre there between 2009 and 2012.

Most of our core 15, however, managed to stay at their positions until the ends of their careers. Good for them.

...But bad for their teams' defenses.

Barry Bonds managed to be pretty decent in left field even in his old age, but not in his final year in 2007 when he was 42 years old and playing on a bad right knee. He rated as one of the worst left fielders in baseball.

Likewise, Wade Boggs went from being solid to being a liability on defense at third base in his final season. He also had a knee issue to blame for his bad defense.

Among the rest, Rickey Henderson, Larry Walker and Kenny Lofton all had issues in the outfield once they got older. Henderson's defense in left field was inconsistent as far back as 1991, and it certainly didn't get better as he got older. Walker, once one of the game's great right fielders, wasn't so great in his final two seasons. Lofton, once one of the game's great center fielders, also struggled on defense in his final two seasons.

Rafael Palmeiro was once one of the game's better first basemen, but he too lost his edge in his final years. After strong performances at short in the late 1990s, Barry Larkin's defense was an issue in his final seasons.

Even Pudge Rodriguez, one of the great defensive catchers of all time, had his issues in his final years. Between 2007 and 2010, his caught-stealing percentage was much closer to the league average than it used to be. It did rise again in 2011, but he only caught 34 games.

If age could do a number on Pudge, then it's no wonder it got to Roberto Alomar and Andruw Jones. Alomar's defense slipped in his final four seasons, and Jones spent the final five seasons of his career bouncing around all over the outfield and DHing (another "Alas!" narrative).

And here's where we cue up another "And on and on it goes." The narratives are many, but the point is simple enough. When players get older, it's not just their bats that are doomed. Their gloves are going to go too. When it happens, it's time to get a hammer and nail out and prepare for the hanging of the spikes.

Granted, there are exceptions here and there. You'll notice that Jeff Bagwell wasn't part of the above discussion. That's because he continually rated as a solid defensive first baseman from his first season in 1991 to his last season in 2005, a hat-tip worthy feat.

Bagwell may have been put in the same boat as the others had his career reached a natural conclusion, however. He called it quits due to a series of shoulder issues that overcame him in '05 and forced him to retire a year later.

And therein lies our final and most crucial checklist item. When a player can no longer hit, run or field, his numbers will say so. But when the end comes, a player's body will say so just as loudly as his numbers.

Old and Beat Up?

Some very complex studies have been done on when ballplayers reach their peaks. J.C. Bradbury did one for Baseball Prospectus that concluded that players peak around the age of 29 or 30. Mitchel Lichtman of Hardball Times says the true peak age is more like 28.

Whatever it is, it's somewhere in the general neighborhood of 30. The further players get beyond there, the more ancient they are.

By baseball standards, the least ancient of our core 15 was Jeff Bagwell, who played through his age-37 season. After him, Larry Walker and Manny Ramirez were the least ancient, as they made it to their age-38 and age-39 seasons, respectively.

Everyone else we've looked at made it at least to their age-40 season. Rickey Henderson made it to his age-44 season, for crying out loud. Only those blessed either with the blood of Numenor (a reference nobody will get) or by the baseball gods make it that far.

Of course, it's not just age that should drive an elite hitter into retirement in addition to the things we've looked at. To paraphrase and totally botch one of Indians Jones' great quotes, it's the years and the mileage.

With a little help from Baseball Prospects' injury database, here's a look at the surgeries and disabled list stints our 15 players collected during their careers.

The total count here: 33 surgeries and 96 trips to the disabled list. If such a stat existed, that would probably give these guys a composite IORP (Injuries Over Replacement Player) somewhere in the six to seven range.

The only guy who escaped both a surgery and a DL stint is Rafael Palmeiro, and we know from his steroid suspension in 2005 that he may not have been keeping his body healthy in natural ways. Whatever the explanation, he's clearly the exception to the rule, and the table doesn't even tell the whole story.

As you'd expect, some guys started piling up injuries later in their careers. Barry Bonds and Wade Boggs both had their right knees operated on. Jeff Bagwell's right shoulder needed two major surgeries. Cal Ripken, he of non-Black Sabbath and non-Robert Downey Jr. Iron Man fame, had lower back surgery towards the end of his career.

Then there's the nagging injury crew. Chipper Jones and Ken Griffey Jr. certainly belong in that, as Jones was constantly battling injuries in the final year of his career and Griffey's health was in a constant state of duress starting in 2001 (Alas!). Frank Thomas' right thigh was prone to strains in his final seasons. Barry Larkin also dealt with leg strains.

Then there are guys like Pudge Rodriguez. You'd think that five DL trips sounds low for him and that surely he was hurt more often than that, and you'd be right. Pudge didn't end up on the DL very often, but he was injured pretty much constantly. It was a catcher's life for him.

And, in general, it was a baseball life for all of these guys. It's not a savage sport—looking in the general direction of football, boxing and MMA—but a 162-game grind year after year after year takes its toll and leaves its marks. These marks tend to require Band-Aids, stitches and pain meds, and players who stick around long enough are going to know the routine more than most.

Excepting Palmeiro, hitters we've had our eye on can vouch, and they should also be able to vouch that there comes a time when a player's body just can't hack it anymore. They can either try the whole mind-over-matter thing, or they can save their bodies for things like golf, cycling or beer-brewing in retirement.

Final Thoughts

So that's pretty much it. Superstar hitters should hang up their spikes when they can't buy a hit, can't hit the ball hard, run or field, and there's no point hoping they'll be able to do any of these things when they're old and beat up.

Hey, I warned way back when that it wasn't complicated. In fact, in a day and age when every baseball analysis piece reads like an instruction manual for assembling a nuclear submarine, I suspect this piece probably reads like "Goodnight Moon."

But this is a case where simplicity is both totally necessary and totally appropriate. Baseball is a complicated game, but it does have a relatively simple heart. And indeed, it doesn't get much simpler than hit ball, run bases, field ball, be young, stay healthy.

Hence the reason why these things are all that need to be on a retirement checklist. If a ballplayer is old and broken and he can no longer satisfy even the most fundamental parts of the game, then there's no point in trying to play it anymore. It's time to hang up those spikes and go invest in a pair of slippers instead.

Note: Stats courtesy of Baseball-Reference.com unless otherwise noted.

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