Between 1995 and 2013, Mariano Rivera was the gold standard when it came to the special breed of ballplayers asked to take the seams at the ends of baseball games. We are fortunate, in that no one truly doubts Rivera's mastery of the ninth inning (and beyond). He is -- by general consensus -- considered the greatest late-game pitcher in history, and there's plenty of statistical muscle to back that assertion up.

Between 1995 and 2010, there was another late-game reliever excelling. Actually, there were several. But for that particular stretch of time, there was one pitcher doing things that Rivera did, except perhaps not quite as frequently. That pitcher wasn't Trevor Hoffman, though he's the one guy in that time period who carried a reputation close to Rivera. It was Billy Wagner.

Wagner wasn't like many relief pitchers in his time. First, he was a left-handed closer -- at least eventually -- which was, and still kind of is a rarity. Closers need to be able to wipe out hitters on both sides of the plate. Second, Wagner was tiny. He was often listed at 5'10", but I feel that was maybe a little generous. Lastly, he threw harder than just about anyone I'd ever watched, save maybe Randy Johnson.

Billy Wagner was unique, but beyond being unique, he was really, really good. He was a strikeout machine, capable of blowing his pitches past just about anyone in any situation. His fastball was a legend, and his slider was enough to keep hitters off-balance, at the least.

Personally, I think Wagner did enough in his 16 MLB seasons to warrant a place among the game's finest in Cooperstown.

Now, if you're a person who believes that relievers don't really have a place in the Hall of Fame because, well, most of them are failed starting pitchers ... then this article isn't really for you. That's an argument I'm not looking to confront here. No, relievers aren't as valuable as starters. Yes, most good starters could also be good relievers. But I'm a believer that performance trumps potential, and that every great role in baseball deserves a place in the Hall.

So, if you believe that relief pitchers belong in the Hall (where right now, only four real relievers reside) -- as I do -- then the idea of Wagner joining them isn't far-fetched at all. The current relievers in the Hall are Hoyt Wilhelm, Rich "Goose" Gossage, Rollie Fingers, and Bruce Sutter. Wilhelm and Gossage are kind of no-brainers in some ways -- both guys threw tons of innings and carry the third- and fourth-best JAWS scores among relief pitchers (behind only Dennis Eckersley and Rivera). Their Baseball-Reference WAR and JAWS numbers are in the forties and high thirties, respectively, and no one else outside the Hall (or named Rivera) comes particularly close.

Name IP bWAR** JAWS** fWAR ERA- FIP- RE24 K% Billy Wagner 903.00 28.1 24.0 23.6 54 63 201.25 33.2 Mariano Rivera 1233.66 57.1 43.0 39.9 46 61 367.21 23.3 Trevor Hoffman 1089.33 28.4 24.0 23.0 71 75 181.58 25.8 Lee Smith 1252.33 29.6 25.4 26.5 75 73 172.64 23.4 Goose Gossage 1578.00 42.0 37.0 27.8 76 82 166.9* 20.8 Hoyt Wilhelm 1840.66 47.3 37.1 20.5 68 83 262.8* 17.7 Rollie Fingers 1553.33 26.1 22.7 22.7 82 81 152.6* 19.3 Bruce Sutter 1042.00 24.6 24.6 20.8 75 78 117.06 20.3

* - These historical RE24 numbers come from B-Ref, ** - bWAR / JAWS numbers include time spent as a starting pitcher

Fingers brings the same huge innings (1,701.1 IP) as the other two guys, but doesn't have nearly the bWAR or JAWS chops as Gossage or Wilhelm. He's actually 26th among "relievers" by JAWS, behind guys like John Hiller and Kent Tekulve, despite all those innings. I'm not certain he belongs in the Hall for any reason other than his mustache, but here he is.

Bruce Sutter is another guy who maybe doesn't come close to Wilhelm, Gossage, or Rivera in terms of overall resume. He was very, very good, but he only rates 17th among relievers in JAWS (22.7), and possesses a bWAR of only 24.6, matching his JAWS rank exactly. That's not to say Sutter wasn't good, or even great -- he was -- but he's very much like Dan Quisenberry or Joe Nathan in those two measures.

Of the existing HoF relievers, Wilhelm and Gossage sit in one tier, and Fingers and Sutter sit in another -- at least when it comes to "classic" HoF stats such as bWAR and JAWS. And Billy Wagner? Well, he sits in that same tier as Fingers and Sutter, along with several other relievers like Quisenberry and Lee Smith.

Wagner possesses a bWAR of 28.1, which is better than both Fingers and Sutter. Wagner also possesses a JAWS of 24.0, which is in between those two pitchers. Actually, his numbers in bWAR and JAWS are nearly identical to contemporary Trevor Hoffman (bWAR 28.4, JAWS 24.0). But these two numbers are both (at least in part) counting stats, and Wagner threw fewer innings than Fingers, Sutter, and Hoffman. Wagner threw fewer innings (903 IP) than anyone on the JAWS relief pitcher leaderboard until you get all the way down to Jonathan Papelbon at 33rd.

So bWAR is good, and JAWS is good, but how about other measures of reliever quality? What about saves?

...

Let's not use saves. There are tons of reasons, but the simplest one is that the save is kind of archaic, and it doesn't actually represent the leverage of a pitching situation. We can get into a more in-depth explanation some other time. #killthesave

Instead, let's look at another Wins Above Replacement option: FanGraphs Wins Above Replacement. fWAR is great in that is measures something slightly different than bWAR, and there are good reasons to use it over smaller samples than bWAR for pitchers. By focusing on the defense-independent variables of strikeouts, walks, and home runs allowed, we get a fine picture of what the pitcher could truly control.

And by fWAR? Wagner's a giant.

Among pitchers with 700 or more innings pitched, Wagner sits fourth all-time with a 23.6 fWAR, behind Rivera, Gossage, and Lee Smith. And again, this is a counting stat. Wagner put up that many wins despite throwing at least 330 fewer innings than any of those names ahead of him. The guys below him on the leaderboard (Hoffman, Fingers, Doug Jones) all have more innings pitched. Wagner was better than those pitchers, at least slightly, in both the aggregate, and on a rate basis.

Speaking of rates, what about his ERA, or his FIP, when compared to league-average and era? We can use ERA- and FIP- to pick out where Wagner falls on the spectrum of relievers when we take into account the league.

As you might guess, Rivera is No. 1 all-time, but Wagner is No. 2 when it comes to ERA- (among relievers with 700 IP). His ERA- of 54 puts him nearly 50% better than league average in terms of run prevention over his career as a reliever. FIP- is nearly as kind, putting Wagner at No. 2 behind Rivera with 63, compared to Mariano's 61. When you take into account the league and era, there's an argument to be made that Wagner was the second-best relief pitcher -- on a rate basis -- of all time.

Finally, we should talk about RE24. A few months back, Ryan Morrison made a nice argument why RE24 is a great stat for determining the quality of a relief pitcher's season, or career. There's lots of places to read about what RE24 is -- like Ryan's article -- but the short form is that it is a (1) counting stat that (2) compares a pitcher's performance to average (3) when taking into account the run expectancy of any situation. The higher the number, the better the pitcher did at reducing a situation's run expectancy.

Sure enough, Wagner also sits at No. 2 all-time here as well, at least among relievers, by FanGraphs's flavor of RE24. His RE24 of 201.25 is little more than HALF of Mariano Rivera's astonishing RE24 of 367.21, but it tops Gossage (197.48, 166.9 in B-R's flavor), Hoffman (181.58), Lee Smith (172.64), and stealth all-time great Joe Nathan (169.18). Once again, take into account Wagner's number of innings pitched, far fewer than any of the folks near him on the leaderboard, save Nathan. To be fair, though, Hoyt Wilhelm could be No. 2 is you prefer Baseball-Reference RE24.

There's a very compelling argument to be made that, on an inning-by-inning basis*, Wagner is the second-greatest relief pitcher of all time. The indexed versions of ERA and FIP make that argument. fWAR makes that argument. RE24 makes that argument.

And so I guess that's the crux of my argument. If you're interested in lights-out ability -- perhaps at the expense of a number of innings pitched -- then Wagner has a stronger case than Sutter, than Fingers, and maybe even than Gossage. That makes him Hall-worthy, in my book. His case is also probably better than Trevor Hoffman if you throw out saves.

Other pitchers may have thrown more innings, or have had more of a defining characteristic ... a game-changing pitch in the case of Sutter or a game-changing face-caterpillar in the case of Fingers, but they didn't have Wagner's effectiveness. And that's why, perhaps, he deserves his own spot in Cooperstown.

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All statistics from FanGraphs and Baseball Reference.

Bryan Grosnick is the Managing Editor of Beyond the Box Score. You can follow him on Twitter at @bgrosnick.