Matt Carpenter, Regression, and the New Aging Curve

Last year, Matt Carpenter was great. If you're reading this blog, (and saw the other two posts about him today), it is likely you are already aware of this fact, but excuse me while I drool over him some more. In the entire league, Carpenter finished sixth in fWAR, ahead of Evan Longoria, Walk Machine Joey Votto, Chris Davis, and even Robinson Cano, among numerous others. His wRC+ placed him 13th overall and first among those who play his position. Likewise, his AVG and OBP both led the pack, while his SLG and wOBA fell second behind Cano.

Carpenter's 2013 was also great by historical standards. Since 1990, his 7.0 fWAR total placed him 17th among his peers at 2B, while his 147 wRC+ places in a tie for tenth with 2002 Jeff Kent. Further, he set the record for Doubles in a season by a lefty, breaking Stan Musial's mark which stood since 1953. In a low run-scoring environment, particularly for Second Basemen, Carpenter's prowess with the bat was remarkable.

To nearly everyone, however, this performance came from nowhere. In the minors, Carpenter's play indicated a player who was extremely patient with little power, and to suggest in his second full season in the big leagues he would put up league-leading numbers is outrageous. Now that he has done this, though, what can we expect from him going forward?

Under the traditional hitting aging curve, it was expected for a young player to reach the majors in their early 20s and continue to improve until their mid-to-late 20s when the player's performance would peak, following which the player would continue to decline until retirement. Recently, though, the evidence suggests a post-steroid era shift in the aging curve, as examined by Jeff Zimmerman on Fangraphs, in two parts. The crux of the pieces can be condensed into this paragraph (though the whole of both of them are worth a read):

Once a hitter makes it to the majors, he doesn’t really improve. In the past, people used to hope for improvement and growth as the player aged. These days, people should expect to see the player performing at his career best immediately.

So, what does this mean for Carpenter? Well, even if one was not factoring in the aging curve, the expectation would be for his performance to decline, from regression alone. Additionally, under the old, steroid-era aging curve, he would be expected to already begin his decline phase this season. Therefore, it may seem the new aging curve doesn't have anything new to tell us about Carpenter's prospects for next season. However, Zimmerman also posits that the reason the aging curve shifted was due to the increased information surrounding prospects and their development, allowing teams to better know when a player is ready to contribute at the major league level. Further, this shift was only delayed by the propagation of steroids, and that before them this shift was already taking place.

Given this, might we expect Carpenter to show the sort of performance plateau younger players have recently? To attempt to predict this, I used the Baseball-Reference Play Index, searching for players who had a late debut (26-30 years old) and at least a six bWAR season within their first three seasons. By these parameters, there are 17 results including Carpenter, as follow.

1       Josh Donaldson   2013 27
2       Matt Carpenter   2013 27
3        Brett Gardner   2010 26
4          Chase Utley   2005 26
5        Ichiro Suzuki   2001 27
6         Rick Wilkins   1993 26
7         Kenny Lofton   1993 26
8         Dave Hollins   1992 26
9           Wade Boggs   1984 26
10          Don Buford   1965 28
11           Pete Ward   1964 26
12     Jackie Robinson   1949 30
13        Johnny Pesky   1946 27
14   Snuffy Stirnweiss   1945 26
15        Earl Averill   1931 29
16        George Stone   1906 29
17          Art Devlin   1906 26 

For our purposes, the more recent the player, the better, so I decided to cut the sample off at the 1980s, due to the other factors which could keep a player off the field in the earlier eras of baseball. This leaves us with a sample of eight players, although one of those is a player whose performance came last year, meaning he is not useful to attempting to predict what Carpenter may do in the future. Let's examine the seven remaining players and how they performed going forward.

Unfortunately, for many of the ones I narrowed it down to by recency, the similarity isn't there. Kenny Lofton and Wade Boggs were both productive almost immediately once they were called up at 24, and quickly began having six and seven WAR seasons. Neither fit the late debut parameter, and are removed. Ichiro doesn't compare well to Carpenter either, as his late debut simply came because he played in Japan for so long. Chase Utley goes along with Boggs and Lofton as a 24-year old debutante who quickly became productive and awesome.

This would leave us with just three players to examine, so I opted to add the older players whose breakout seasons came at a later age, meaning Don Buford, Johnny Pesky, Earl Averill, and George Stone. Pesky can be eliminated, as he was serving in the war for what would have been his 24-26 year old seasons. This leaves us with Buford, Averill, Stone, Hollins, Wilkins, and Brett Gardner.

Buford was signed out of USC as a 22 year old and spent the majority of four seasons in the White Sox minor league system before making his pro debut in a cup of coffee in 1963. In his first full season on the Sox' roster, Buford hit .262/.337/.348, good for an OPS+ just below league average at 94. This, in combination with slightly above average defense at second and third, was good for 2.5 WAR. The next season, Buford broke out, hitting .283/.358/.389 and an OPS+ of 120. With equally improved defense, these numbers meant 7.0 WAR. This is perhaps the best comparison for Carpenter, as along with playing the same positions, Buford's hitting profile is also similar to Carpenter, with more gap power than HR power and relatively balanced SO and BB. Over the next couple of seasons, Buford remained productive but wouldn't return to the level he flashed, with WAR totals of 4.5, 3.0, 4.8, and 4.8 over the next four seasons, eventually becoming ineffective in his age-35 season, following which he played in Japan.

Averill debuted as a 27-year old in 1929 with a line of .332/.398/.538 and OPS+ of 136, worth 4.2 WAR with below average defense in CF. The following year, he would replicate his performance. In his third season, the bat production would jump to the tune of a 150 OPS+ and, still playing CF, was worth 6.1 WAR. Averill's offensive contribution was more based on power, with the jump from 19 to 32 HRs being the main difference between his first two seasons and his third. In the following seasons, his power would fluctuate, as would his WAR, though he would still remain productive with totals of 4.7, 3.8, 6.8, and 3.6. His last productive season came as a 36-year old, though he would remain in the majors until playing eight games as a 39-year old. He would eventually be elected into the Hall of Fame by the Veteran's Committee.

Stone's true major league debut came as a 28-year old, and he was immediately effective with an OPS+ of 145 and a WAR of 4.8. If there had been an MVP award around for his second pro season, he likely would have won it, leading the league in AVG, OBP, SLG, and TB. His performance was so great, in fact, it was nearly twice as prolific as the league average, with an OPS+ of 193. All this was worth 8.7 WAR. The performance would continually slip each year going forward until he was out of the league four years later.

Hollins spent parts of his 24-and 25-year old seasons in the majors. The level of play in the latter--worth 1.5 WAR in just 56 games--was enough to earn him a shot going forward, where he posted an OPS+ of 137, good for six WAR while splitting time between first and third. In that season, he hit 27 HR, a level he wouldn't reach again in his career. In the following season, Hollins remained healthy and productive with a 3.4 WAR season. I assume injury must have followed, however, because in just 44 games he was below replacement level the next season. Once healthy again, he returned with seasons of 1.6, 4.2, and 3.5 WAR. He would last another four seasons, though none were productive. At the 1996 trade deadline, Hollins was traded to the Mariners for a PTBNL who would later become David Ortiz. Then, to the dismay of Cardinals fans everywhere, Ortiz would go on to join the Red Sox and have a very productive career, particularly in the postseason. Cuss.

Wilkins, like many on this list, had two seasons of average performance before breaking out in his third season. This came in part due to a jump in power, with 30 HRs versus just six and eight his first two. In fact, Wilkins would only break double digits one other time in his career, in 1996. This is primarily due to the lack of playing time, possibly due to health and possibly ineffectiveness. Regardless, he would surpass one Win the following season, then one final time in 1996. He would play in several more seasons, though break 20 games played only once.

Gardner is a fantastic defender whose offensive performance has been inconsistent thus far. Even without the offense, his defense has been good enough to remain a valuable player. Once he is able to combine the defense with even just a slightly above average offense, seasons like 2010 are possible, when Gardner had 7.4 WAR, almost evenly split between offense and defense. In the seasons following, he has been a 4-WAR player, except while injured in 2012.

Returning to the main question of this post, what we can expect out of Carpenter next year and beyond, obviously there will be a drop off from last season. The ZiPS projection for him feels too low, and I'd be more surprised if he hit .272/.351/.413 than if he hit above it. The Steamer--and similar Oliver--projection, at .291/.373/.442, seems the most likely, and it wouldn't be out of line with any of the historical examples' follow-up seasons. Matt Carpenter was great in 2013, and probably won't be great in 2014, which is the reality of player performance and regression. Carpenter will continue to be good, possibly really good, but definitely cheap. The Cardinals should feel really lucky or really smart for having him develop this way.