Basic Hitter Platoon Splits 2002-2012

Baseball fans like to talk about splits. Some splits are more useful than others. Platoon splits are particularly interesting because they can be used both in evaluating players and in thinking about strategy. As has been emphasized elsewhere, observed platoon splits can vary quite widely from a player’s true platoon skill. For that, we need to know the platoon skill of the population from which he comes, at least generally speaking. The first step for doing that is to see what the overall platoon split of hitters is in any given year. Looking at that also leads to other interesting questions.

A couple of years ago, I did a similar post. Since I was updating that information for myself, I thought it would be worth sharing. This post will not contain any grand conclusions, just the data and some observations.

Hopefully the reader will forgive some less-than-artful tables. I went for relatively quick-and-easy, which in this case did not lead to a particularly brilliant tabular aesthetic (for example the percentage columns having two decimal places. Ah, the joys of using Google Docs).

Some brief explanations: I use platoon data since 2002 from our database. Each row is for a separate season. As for columns, “wOBAvL” and “wOBAvR” should be self-explanatory; “wOBA” is he overall wOBA for that year in the cases looked at (more on this in a bit), “%vLHP” is percentage of plate appearances versus left-handed pitchers examined (since plate appearances versus southpaws are what one regresses against when estimating hitter platoon skill), and “Split%” is the percentage of the split compared to the overall wOBA, since that is what is measured when projecting platoon skill.

When I mentioned “cases looked at” I simply meant that I excluded certain things. I naturally excluded pitchers as hitters. I also excluded the cases where batters pitched from the wrong side of the plate, e.g., switch hitters giving up the platoon advantage as they sometimes do against knuckle-ballers. Those occurrences are not too frequent, but it is worth excluding them.

[NB: Those who look carefully will notice some slight discrepancies in some ostensibly shared data between the 2010 post and this one. Without getting in to every little detail, most of that is probably due to changes in way wOBA has been calculated since my 2010 post and also some improvements I have made (e.g, excluding sacrifice hits from the population, as they are not included in wOBA and slightly skewed denominators in the older post).]

This first table is for left-handed hitters:

LHH	wOBAvL	wOBAvR	wOBA	vLHP%	Split%
2002	0.318	0.350	0.343	22.31%	9.33%
2003	0.317	0.348	0.340	24.66%	9.11%
2004	0.325	0.351	0.345	24%	7.54%
2005	0.314	0.343	0.336	23.09%	8.62%
2006	0.317	0.354	0.345	23.51%	10.72%
2007	0.321	0.351	0.344	24.17%	8.73%
2008	0.316	0.347	0.339	24.69%	9.14%
2009	0.316	0.350	0.342	25%	9.96%
2010	0.312	0.341	0.334	24.64%	8.69%
2011	0.297	0.330	0.322	23.86%	10.24%
2012	0.291	0.332	0.321	26.65%	12.77%

Left-handed hitters typically have bigger platoon splits than right-handed hitters. While left-handed hitters almost always hit better as a group than right-handed hitters (having the platoon advantage most of the time is big part of that), in the last couple of years, for whatever reason, their overall advantage has decreased rather dramatically, even though left-handed hitters are not facing that many more southpaw pitchers than in the past. What has changed: in 2011 and 2012 the platoon split of left-handed hitters has increased a great deal over previous seasons, with the 12.8 percent split in 2012 being easily the largest for lefty hitters in the period examined.

RHH	wOBAvL	wOBAvR	wOBA	vLHP%	Split%
2002	0.335	0.323	0.326	26.77%	3.68%
2003	0.349	0.324	0.331	28.80%	7.55%
2004	0.346	0.327	0.333	29.12%	5.71%
2005	0.347	0.322	0.329	29.34%	7.59%
2006	0.349	0.327	0.333	29.23%	6.60%
2007	0.358	0.324	0.334	29.13%	10.18%
2008	0.346	0.323	0.330	30.10%	6.97%
2009	0.345	0.325	0.331	29.03%	6.05%
2010	0.338	0.319	0.325	29.75%	5.85%
2011	0.339	0.313	0.320	28.37%	8.12%
2012	0.337	0.313	0.321	31.96%	7.48%

As expected, right-handed hitters display a much smaller split than left-handed hitters, although it has increased league-wide after the low of 2010. One can see that the shrinking gap between right- and left-handed hitters in recent years is mostly because lefties have gotten worse and righties have stayed the same the last couple of years.

Finally, the switch hitters (a negative percentage means that as a group they hit lefties better than righties in that particular season):

BHH	wOBAvL	wOBAvR	wOBA	vLHP%	Split%
2002	0.312	0.328	0.324	25.78%	4.94%
2003	0.330	0.325	0.326	25.94%	-1.53%
2004	0.324	0.329	0.328	27.7%	1.53%
2005	0.320	0.327	0.325	26.09%	2.15%
2006	0.326	0.336	0.333	26.39%	3%
2007	0.331	0.330	0.330	27.24%	-0.3%
2008	0.336	0.332	0.333	28.85%	-1.2%
2009	0.335	0.327	0.329	27.15%	-2.43%
2010	0.313	0.315	0.314	28.55%	0.64%
2011	0.319	0.322	0.321	27.64%	0.93%
2012	0.312	0.317	0.316	29.66%	1.58%

Switch hitters are both less and more interesting than the other two groups. They are less interesting in the sense that switch hitters vary more widely from hitter to hitter, and thus require much less regression than left- and right-handed hitters. While regression should be done, the observed performance becomes relevant in far few plate appearances than for lefties or righties.

Switch hitters are more interesting because of that variance. Although as a group there is not much to say about them, individuals are more amenable to specific analysis. As a group, they have not generally displayed a consistent or large split, which probably means most switch-hitters are being helped by hitting from both sides of the plate. Switch hitters are a group that might be worth more historical investigation.