Scooter Gennett had an impressive 2013 debut with the Brewers. Over 230 plate appearances — about a third of a season — Gennett’s bat produced 31% better than the league average position player (wRC+ of 131), and he combined that with above-average base running and slightly-above average defense. Gennett did so while hitting left-handed, a rare capability in the Brewers lineup.
The one thing Gennett didn’t do well was hit well off his fellow left-handers. In fact, Gennett was a bit of a disaster against left-handed pitching, striking out 32% of the time and managing only a miserable .151 wOBA. Gennett did such a poor job in that one regard that many have proposed putting him into a job-sharing arrangement — or platoon — going forward with a right-handed hitter who would bat against lefties. Some have further advocated signing a utility infielder whose primary purpose would be to give Gennett a platoon partner.
I think this is a bad idea, but it makes for a useful opportunity to talk about platoons and some of the more recent developments involving them.
Let’s start by reviewing how and why platoons exist. The science of platoons is interesting, because it’s an area of strategy on which both old-school and new-school folks agree. Baseball players and managers have long believed that batters hit opposite-handed pitchers better and we have since confirmed, statistically, that they are right. According to Baseball Reference, in 2013 alone, right-handed batters on average produced 8% better than the overall league average when hitting off of left-handed pitchers, and left-handed hitters produced 7% better when hitting off right-handed pitchers. (108 OPS+ vs. 107 OPS+, respectively).
The flip side is that these same batters also struggle by comparison when hitting against a pitcher who throws from the same side from which the batter hits. In 2013, right-handed batters hit 6% below league-average when facing right-handed pitchers, while left-handed batters hit a whopping 19% below league-average when facing left-handed pitchers. (94 OPS+ vs. 81 OPS+). If you want to know why left-handed relievers last forever in baseball, that is it. Some of the game’s best sluggers are lefties who benefit from the majority of pitchers being right-handed. So, the corresponding inability of left-handed hitters to hit left-handed pitchers is the equalizer. In fact, over the past two years, the futility level of left-handed hitters against left-handed pitchers has reached new heights, approaching almost 50 points of wOBA. Losing 50 points of wOBA means that, against an average a left-handed pitcher, Matt Carpenter would become Alex Gordon, and Carlos Beltran would become Gregor Blanco. That’s quite a difference.
Those trends notwithstanding, not all batters have the same platoon split, and it takes a long time for a player’s individual platoon split to stabilize. According to The Book, left-handed batters stabilize their platoon deficit much faster than right-handed batters, but on average it still takes almost 1000 plate appearances to reach that milestone. To give you a sense, Matt Carpenter had over 700 plate appearances in 2013, and even he registered just 222 plate appearances against fellow left-handers. Thus, it takes several seasons for most players to display a trustworthy platoon split. Even then, the split will always tend to keep regressing back toward the league average.
I think these principles make it clear that platooning Scooter Gennett right now would be a terrible idea. Let’s start with the reasons relating to Gennett himself:
(1) Gennett’s woeful numbers against left-handed pitching in 2013 arose from a grand total of 41 plate appearances. For platoon evaluation, this sample size is so small as to be meaningless.
(2) Although Gennett had a platoon split in the minors, it was much closer to the major league average. This is pretty good evidence that Gennett’s true skill in hitting left-handed pitching is significantly better than what he showed last year and will probably improve as he continues to face major league pitching.
(3) People are fond of saying that Gennett’s gaudy production numbers from last year will probably regress. That’s almost certainly true, but then you also must accept that regression will similarly improve his numbers against lefties, probably toward or even exceeding his minor league numbers.
(4) Gennett was only 23 years old last year! The currently-accepted performance peak for baseball players is around 27. Giving up on any important attribute of a recently-arrived, 23-year-old major leaguer is absurd. And if the Brewers do not give Gennett consistent opportunities to hit major-league left-handed pitching, he of course cannot get better at hitting them.
(5) Moreover, we learned above that virtually all left-handed hitters struggle with left-handed pitching, and that left-handed hitters as a whole are getting worse, not better, at hitting the left-handed pitching presented to them. Even if Gennett turns out to have a notable platoon penalty, he would hardly be unique.
(6) Last but not least, people need to appreciate that Gennett’s extraordinary production last year included his problems with lefties. In other words, even with no production against lefties, only two second-basemen in baseball had better overall production per plate appearance than Gennett last year: Robinson Cano and Matt Carpenter. No player is perfect, and if hitting left-handed pitching turns out to be Gennett’s one major weakness, suffice it to say the Brewers will have made out well.
Platooning Gennett would have disadvantages for the Brewers as well. They would have to dedicate a roster spot to a platoon partner, and would have to limit themselves to platoon partners that are right-handed. As a free agency signing, this platoon partner is likely to end up being overpaid for his occasional production, and the development of any farm-system platoon partner would similarly suffer by not being permitted to hit against right-handed pitching. The Brewers would end up with two incomplete players.
Because the Brewers are at best a fringe contender next year, there is no reason for them to withhold opportunities for Scooter Gennett to improve his game. If the Brewers do find themselves in contention come July, they can always rent a right-handed infielder for cheap if the club’s production needs to take temporary priority over Gennett’s development.
In the meantime, the Brewers need to let Gennett take on all pitchers, and see what they have.
Follow Jonathan on Twitter @bachlaw.