Yesterday, I looked at how one of the last seasons of the steroid era (2002) compares to the present one in terms of home runs, total offense, and overall value by position. To summarize the findings of that post briefly: while corner outfielders account for less production now than they did in 2002, infielders and catchers are now responsible for more of it. Moreover, players at the top of the home-run leaderboards now are accounting for a lower percentage of total league-wide homers than in the steroid era. There’s a more even distribution of homers, in other words.

Today, I’ll look deeper into the contrasts between the two seasons, considering performances by different age groups, both for hitters and pitchers. The stereotypical PED user from the early part of this century was a muscled-up player defying age with strong offensive production deep into his 30s. This isn’t just a stereotype, though. It’s supported both by the playing-time and production data from that time period. Baseball has become a young man’s game. The table below features a breakdown of plate appearances by age group both for 2002 and 2017.

Comparing the Steroid Era to 2017 by Age: Plate Appearances Age 2017 % of PA 2002 % of PA Change Through 25 26.5% 18.4% 8.1% 26 to 30 44.3% 46.4% -2.2% 31 and Over 29.2% 35.1% -5.9%

There are a lot more young players now than there were during the PED era. That +8.1% change for players 25 years old an under represents a 44% increase in playing time compared to 15 years ago. While the players likely to be in their prime, from age 26 through age 30, have seen slight decrease in playing time, it’s the league’s oldest players who’ve taken the biggest hit, accounting for 6% fewer plate appearances now.

There’s a pretty good reason for that drop in playing time: the younger players are a lot better than they used to be relative to the rest of the league.

Comparing the Steroid Era to 2017 by Age: Adjusted Batting Age 2017 wRC+ 2002 wRC+ Change Through 25 96 85 11 26 to 30 98 99 -1 31 and Over 96 99 -3

Young players weren’t playing as much 15 years ago because they weren’t as good. One theory might be that they were less likely to be using PEDs due to issues of access, finances, and the presence of minor-league testing. As a result, they couldn’t compete with the veterans who had those advantages. As those advantages have dissipated, though, production among younger players has increased. Take a look at wRC+ by players age 25 and under over the last 40 years.

That large valley in the middle of the graph is the steroid era. After testing began, production from young players returned to the levels at which it had mostly remained before PEDs became prevalent. In 2017, young players are hitting better than almost at any point since just before 1980. Both playing time and offense are up.

Here’s the breakdown in terms of homers:

Comparing the Steroid Era to 2017 by Age: Home Runs Age 2017 % of HR 2002 % of HR Change Through 25 27.7% 16.2% 11.5% 26 to 30 44.4% 47.4% -3.0% 31 and Over 27.9% 36.4% -8.5%

As indicated earlier, the oldest group of these three has recorded 6% fewer plate appearances than in 2002. Their drop in homers is even larger, though. The older group is playing less and packing less of a punch, while younger players are outgunning their increase in playing time. It should be no surprise that this carries over into WAR, as well.

Comparing the Steroid Era to 2017 by Age: WAR Age 2017 % of WAR 2002 % of WAR Change Through 25 28.6% 14.5% 14.1% 26 to 30 49.9% 50.3% -0.4% 31 and Over 21.5% 35.2% -13.7%

WAR from young players has doubled since the PED era, while older players’ share of WAR has decreased by nearly 40%. Some of the change is attributable to the changes in playing time. Overall, though, younger players are better on a rate basis, too.

Comparing the Steroid Era to 2017 by Age: WAR per 600 PA Age 2017 WAR/600 2002 WAR/600 Change Through 25 2.0 1.4 0.6 26 to 30 2.1 2.0 0.1 31 and Over 1.4 1.8 -0.5

Young and old players have essentially flip-flopped in effectiveness. Where once the young players were below average, they’ve now become nearly as good as players in their primes. Older players, meanwhile, once nearly as good as players in their prime, have felt the effect of age-related decline more acutely. This might help explain why aging curves can be difficult and why they change over time. It seems very likely that PED use affected aging and players’ ability to stay healthy and play longer, defying what we thought we knew about aging. That hasn’t been the case this season, as aging players are worse than their younger counterparts — as we’d expect in the absence of chemical enhancement.

The other effect here can be seen in the cost of players in free agency. Dollars spent per WAR seem to be rising to high levels. Some of this is, no doubt, due to increased revenues in the sport. Television contracts have accounted for much more revenue, especially locally. MLBAM and BAMTech, meanwhile, have increased the value of major-league clubs, and some of that money is going to go into player contracts. Those increases alone might not completely explain the rise in free-agent contracts in terms of dollars and WAR. During the PED era, teams could head out to free agency and reliably find useful players to add wins to their ballclub. As the tables above demonstrate, there are now fewer players of free-agent age playing in the majors, and the quality of those players has gone down. With a decreased supply, the cost to buy a win has risen steadily.

We generally focus on hitting when discussing the steroid era, but pitching has changed, too. We know that strikeouts are one majors difference. The distribution of innings from starters to relievers has changed considerably, too, though. Here’s the breakdown of innings from 2002 to 2017 between the two groups.

Comparing the Steroid Era to 2017 in Pitching: Innings Role % of IP 2017 % of IP 2002 Change Starters 62.2% 66.5% -4.3% Relievers 37.8% 33.5% 4.3%

A 33% gap has now been narrowed to 25% when it comes to innings. This is going to reduce offense and increase strikeouts. Relievers aren’t getting more innings just because starters are getting tired. Relievers are getting better. Here are those numbers when it comes to share of WAR.

Comparing the Steroid Era to 2017 in Pitching: WAR Role % of WAR 2017 % of WAR 2002 Change Starters 74.0% 81.2% -7.2% Relievers 26.0% 18.8% 7.2%

Just to put those numbers into better perspective, here’s how they look on a rate basis.

Comparing the Steroid Era to 2017 in Pitching: WAR per 180 IP Role WAR/180 IP 2017 WAR/180 IP 2002 Change Starters 2.1 2.2 -0.1 Relievers 1.2 1.0 0.2

Despite accumulating a greater share innings, relievers have actually increased their effectiveness per inning pitched, too. This seems to indicate that the overall talent level of pitchers has risen. Because the number of starting jobs has remained static, though, the marginal improvement of relievers has been stronger. Potential starters get pushed to the bullpen, where they pitch even better than they would if they were in the rotation. That’s how you get more strikeouts and less offense over the past decade (until the past few years, during the home-run surge).

Here’s what happens when we break the starters down by age.

Comparing the Steroid Era to 2017 in Pitching: Starter WAR per 180 Age SP WAR/180 IP in 2017 SP WAR/180 IP in 2002 Change Through 25 2.1 2.1 0 26 to 30 2.3 2.1 0.2 31 and Over 1.8 2.5 -0.7

It isn’t just aging hitters who’ve experienced a decline in performance since the steroid era. Their pitching brethren have endured an even larger decline. Veteran pitchers were the class of the field back in 2002, but they’ve been relegated to the back of the pack in the present. Unlike hitters, young pitchers were already holding their own back in 2002; nothing has changed in that regard. In terms of usage, we have seen a shift toward the middle, as well, as more and more innings are being gobbled up by players between the age of 26 and 30.

Comparing the Steroid Era to 2017 in Pitching: Starter Innings Age SP % of MLB IP 2017 SP % of MLB IP 2002 Change Through 25 16.5% 23.7% -7.2% 26 to 30 29.0% 24.7% 4.3% 31 and Over 16.7% 18.0% -1.4%

There are about as many aging starters as there used to be, but they simply aren’t as good. Meanwhile, fewer innings are going to young pitchers, perhaps as an attempt to protect their arms. Not all, but some of that, is made up by an increase in bullpen work.

Comparing the Steroid Era to 2017 in Pitching: Reliever Innings Age RP % of MLB IP 2017 RP % of MLB IP 2002 Change Through 25 7.2% 5.6% 1.5% 26 to 30 20.6% 15.5% 5.2% 31 and Over 10.0% 12.4% -2.4%

The “prime-age” pitchers accounted for roughly 40% of innings in 2002; that number has increased to roughly half of all innings this season.

We know there were a lot of players using PEDs back in the late 90s and early 2000s. For the most part, we know what it looked like. We saw a lot more homers everywhere, but especially at the top of the league, from burly corner outfielders. We saw a lot of players — both hitters and pitchers — defy traditional aging curves, playing well into their 30s. That’s what the steroid era looked like. What today and the steroid era have in common is a lot of homers. We don’t see the same bunching at the top of the leaderboards, though. Homer totals are more spread out. We don’t see a certain class of players surpassing historical norms, either. Instead, we observe a bunching at positions and age groups, with typical aging curves returning.

We can’t say for sure that steroids and other performance enhancers aren’t taking over the game again. What we can say is that the power boost we’re seeing now doesn’t resemble the power boost we witnessed in the steroid era. To believe that steroids are playing a major role in the current increase in power, we would have to believe nearly every player is benefiting from that and that the effect has happened nearly overnight after a decade of dormancy. PEDs certainly haven’t been eradicated, but there are far more plausible scenarios backed with a lot more evidence than suspecting that the increase in offense has due to do with chemical enhancements the players are making.