Can Colby Rasmus Hit Lefties?

I’m loathe to discuss the (alleged?) rift between Tony LaRussa and Colby Rasmus. My personal opinion is that the young center fielder should be playing every day, but I don’t have the desire, energy, or efficiency to cover every relevant issue. Joe Posnanski’s take is predictably enjoyable, in particular emphasizing reasons why many people are, well, sick of LaRussa. I imagine that’s a common sentiment, which is why it was good to see it acknowledged in Tim Marchman’s thoughtful “pro-LaRussa” post. One phrase in Marchman’s writeup particularly caught my eye:

Colby Rasmus is a really talented young player who can’t hasn’t hit lefties…

This raised the hackles of many people out there who quickly checked the numbers and pointed out that Rasmus has actually been pretty decent against lefties this season — 102 wRC+ (.323 wOBA) in 102 plate appearances, or a slightly above average hitter. However, he was absolutely dreadful versus southpaws in 2009, with a 28 wRC+ (.218 wOBA) over 115 PA. Despite a good overall line, a .256 career wOBA versus left-handed pitching is absolutely dreadful. But observed performance and true talent are two different things. Does Rasmus really have a problem hitting lefties?

As Marchman acknowledges in the comments to his post, 217 career plate appearances versus lefties doesn’t establish much (I assume that’s why Marchman has “can’t” crossed out in the quote above) — one should regress a left-handed hitter’s observed split against 1,000 plate appearances of league average to get an estimate of his actual platoon skill. After doing so, the estimate of Rasmus’ “true” platoon split still isn’t very encouraging. Using the ZiPS RoS .329 wOBA as a overall baseline, he projects as a .339 wOBA hitter versus RHP and a .297 wOBA hitter versus LHP. Even bumping that projection up to .340, he still only projects as a .307 wOBA hitter versus LHP. I’m not sure if platoon issues are one of the reasons LaRussa has sat Rasmus so often (and Rasmus has actually played seven of the last eight games, so this whole brouhaha may be about over), but if it is,
there’s reasonable evidence to suggest that in this case LaRussa might not be asleep at the wheel.

But back up for a moment: when we say that we need to regress against 1,000 PA of league average performance by LHH against LHP, that means that at 1,000 PA of observed PA vs. LHP, a hitter’s platoon skill is estimated to be “exactly” between midpoint between league average and his observed performance. This sort of regression is the right way to do things, particularly for minimizing error when doing projections for numerous players, but it also means that from just 217 PA, we really know very little about Rasmus’ platoon skil — the estimate is based much more on league average than on observed performance. So let’s dig a bit deeper.

The Book-derived method I use to estimate splits is based on major-league data, so it isn’t clear how platoon skills displayed in the minor leagues translate to the majors. Nonetheless, given the paucity of Rasmus-specific major league plate appearances vs. LHP to go on, let’s take a look at his minor league numbers. A quick glance at Rasmus’ player pages at Minor League Splits (which doesn’t use wOBA) reveals that he actually hit lefties quite well in the minors: .275/.371/.455 versus .278/.364/.496 for righties. That’s a pretty small split. More specifically: in AAA in 2008, he only hit .255/.347/.353 versus lefties, but given that his OPS versus RHP was .250/.347/.417, that’s still a small split for a left-handed hitter. At AA Springfield in 2007, He had a larger split (.839 OPS vs. LHP and .958 vs. RHP), but again, that isn’t a terribly big split for a lefty, and he had almost the same OBP versus LHP (.379) as righties (.381).

As for the major leagues, one should be cautious when splitting up his miserable 2009 and better 2010 because it is already a very limited sample. Of course, as soon as bloggers bring up “small sample size” we almost always go on to talk about the sample anyway, and I’m no different. In 2009 Rasmus pretty much did everything horribly versus left-handed hitters, although his .187 BABIP does seem to be quite unlucky. I’m not ready to say (particularly given the minor league numbers) whether Rasmus “learned” something about lefties between 2009 and 2010 or whether it is just regression, but there is obvious improvement almost across the board. His line drive rate versus LHP and RHP is the same (19%). His walk rate versus lefties (8.8%) is above the overall league average (8.5%). The power versus righties has improved, and while Rasmus is being criticized for his high overall 2010 strikeout rate (33%), his K rate versus lefties (29.7%) is actually better than his K rate versus righties (34%).

On its own, this breakdown of a small sample some of Rasmus’ split peripherals by season doesn’t tell us much. However, given the platoon skill he displayed in the minors, it does suggest that 2010 might be more reflective of his abilities against lefties than 2009. I don’t know what issues Tony LaRussa has with Colby Rasmus, but a careful look at the numbers suggests that concerns about Rasmus’ ability to hit left-handed pitching are overblown.