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July 3, 2009

Checking the Numbers

Contextual Platooning

by Eric Seidman

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Nothing grinds my gears within the realm of sabermetrics as much as the avoidance or misuse of context. For whatever reason, something simple like using the appropriate frames of reference has become the type of analytical tool that makes sense to implement only when it furthers a predetermined point. In fact, if nothing else is taken away from this article, heed the following warning: never trust any conclusions drawn from performance splits if the league average of that split is absent from the same analysis. If the goal involves evaluating pitcher performance with the bases empty vs. with ducks on the pond, the results of each individual must be compared to the aggregate league split before anything of interest can be parsed. The same can be said for gleaning useful information from platoon splits, which happens to be our topic du jour. Platoon splits are certainly existent, but before suggesting that certain players should split duty at a position, we need to understand what the data really explains and the appropriate context in addition to potential shortcomings for which to look out.

At its deepest root, platooning refers to using multiple players to man a position. Nowadays, 'multiple' can be more accurately represented by el numero dos, as platoons primarily consist of two players providing the production that other teams seek from one individual. These platoons are generally contingent upon handedness; the right-handed hitter faces southpaw pitchers, and vice versa. From an overall standpoint, studies have proven it undeniable that hitters perform better against opposite-handed pitchers than their same-handed brethren. From 2003-08, here are the yearly figures against same-handed pitchers:


Year SHP-REqA  OHP-REqA
2003   .757     .793
2004   .770     .797
2005   .752     .786
2006   .767     .807
2007   .757     .801
2008   .751     .789

The data clearly indicates that, overall, hitters fare worse against pitchers from the same side. Split even deeper, though, and the effects are more pronounced amongst lefties. One line of reasoning that surfaces quite often with regards to the more substantial splits for lefties offers that northpaws account for approximately 70 percent of all plate appearances; while righties get to see same-handed pitchers with great frequency (allowing adjustments to be made), lefties are not necessarily privy to the same opportunities. With such relatively few plate appearances against same-handed pitchers, the lefty-on-lefty matchup is a bit more foreign than its right-handed counterpart. Platoons also become somewhat difficult to implement with regularity because of the current fashions in roster space assignments; given the choice, teams will opt to employ the talented solo artist as opposed to the dynamic duo. In Strat-o-Matic leagues (especially the superstar league in which I partake), such dynamic duos are much more relevant, because a well-executed platoon can come close to creating a makeshift Pujols.

Having covered the background of platooning, there are a few major points to hammer home, the first of which reiterates my earlier plea: players must be compared to the league when discussing performance splits. The league… not themselves… which is a point many seem to gloss over. Just because Player A posts an 1100 OPS vs. opposite-handed pitchers and a 750 OPS against his same-handed opponents does not automatically trigger an invitation to the platoon party to be mailed; this hypothetical player must first be compared to the league in both areas. Comparing a player to himself tells us nothing of importance other than his own trends. It fails to incorporate context, and we are left wondering how the 1100 stacks up in contrast to the rest of the league's performance against opposite-handed pitchers, and how that 750 OPS against same-handed hurlers compares to the rest of the league against pitchers from the same side.

All of which brings us to Ryan Howard, a popular candidate mentioned in platoon discussions in several different venues by a number of different columnists, including on this very site. My goal in discussing Howard is not to refute anything previously written, since some of the underlying logic makes a lot of sense, but rather to introduce the appropriate context to the discussion and then see what the data indicates. Essentially, those of the opinion that the former MVP should be platooned point out his drastically different handedness results. And they would be correct, as Howard has a .303/.409/.657 line against righties, with a triple-slash performance of .227/.308/.452 against lefties. When birthday-suited up, these numbers clearly lead to the conclusion that Howard stinks against same-handed pitching.

Using Howard himself as the context, however, misses the boat and instead works similarly to price anchoring on infomercials. The commercials will display a product and explain how it used to cost $100 but can be had now for just $35; stacking up the $35 to the $100 is not the correct basis for comparison, as the $35 should be compared to the current price of other, similar products elsewhere, and not to its reported former price. After calculating the slash lines for hitters against same-handed pitching in each season, here is how Howard has fared relative to the rest of the league:


Year   PA  SHP-REqA  lgSHP-REqA  Delta
2005   63    .429      .752      -.323
2006  225    .925      .767       .158
2007  246    .839      .757       .082
2008  265    .762      .751       .011

Self-context suggests that Howard is a perfect platoon candidate. The appropriate context pegs Howard as well above-average against opposite-handed pitchers, and at worst, a league-average hitter against the same-handed. As was mentioned before we got into Howard's specifics, some of the logic to platooning a player who hits like this makes sense. After all, first base is a premium offensive position, and the goal should be to maximize production when possible. If a team gives 70 percent of its plate appearances to Howard-since righty pitchers accrue that percentage of playing time-it stands to reason that a suitable sidekick could be found to handle the 25-30 percent of plate appearances with lefties toeing the rubber.

However, with the full knowledge that Howard has been above-average or average against same-handed pitchers, might there be better platoon choices on his own team, let alone the rest of the league, especially given the expense of using a roster spot on a platoon partner? The table below shows current Phillies starters who don't switch-hit, and their Raw EqA (sans stolen-base components) against same-handed pitching in 2007-08, as well as the same metric for the rest of the league, and the differential:


Hitter        SHP-REqA lgSHP-REqA  Delta
Chase Utley    .911      .755       .156
Jayson Werth   .783      .755       .028
Raul Ibanez    .779      .755       .024
Pedro Feliz    .699      .755      -.056

Howard may be trending downwards against same-handed pitchers, but the table indicates that he might not even be the player best suited for shared duty on his own team. This segues into the next major point of contention-the data simply isn't as reliable as we think. The Book: Playing the Percentages in Baseball dedicated an entire chapter to this topic, and Dan Fox followed up on the point in 2006, but allow me to summarize some of their findings. First, platoon splits are normally distributed, lending themselves more to chance than individual skill. When a dataset is normally distributed, in the form of a bell curve, we cannot say that incredibly good or bad marks are not the direct results of chance, since such distributions call for certain percentages of its sample to exceed two or three standard deviations of the mean. This is not to say that all platoon splits are derived from chance, but rather that separating skill from chance proves to be a much more difficult task, mainly due to sample-size issues.

With such small plate-appearance samples accrued each season, investing in the stock of platoon splits is not very prudent. Dan used split-half reliabilities relative to career handedness splits to show very unstable performance, and my favorite toy, the intra-class correlation, concurs. If we usually require 1,500-2,000 plate appearances over three years from a player before determining a semblance of his true talent level, why on Earth would 125 trips to the dish in three straight seasons against a specific side of the mound convince us of productivity levels? Simply put, platoon splits are consistent in the aggregate, but not from an individual perspective. Because of this fact, in conjunction with the sample-size issues, Tango, Lichtman, and Dolphin concluded that the platoon split of an individual player had to be massively regressed to the mean to get an accurate indicator of the true differential. For righties, 2,200 plate appearances worth of regression needed to be factored in, with 1,000 plate appearances for lefties.

Overall, platoon splits might be the byproduct of chance, are accrued in small pools of plate appearances incapable of determining statistically significant consistency, and must be heavily regressed before any real talent level can be deciphered. With these characteristics in mind, I fully support the suggestion of relying more heavily on scouting information than the numbers to determine a hitter's ability against same-handed pitching. If a scout can note a specific player struggling in terms of bat speed or perceived pitch recognition against a same-handed pitcher, and the evaluations are corroborated by a plentiful bounty of trustworthy sources, I would be more inclined to base decisions off of this information than a heavily-regressed, potentially inconsistent, platoon split. The takes of legitimate scouts can indicate the roots of certain struggles or changes in approach against same-handed pitching, the sorts of thing that could lead to upticks or downturns in a player's performance. The best information is the most accurate, and in this case, scouting information likely has an advantage over the data.

Platoons certainly exist at the major league level and, in the aggregate, hitters definitely perform better against opposite-handed hurlers, but the data used to evaluate such performance needs to be viewed with the appropriate contextual lens-the league, not the individual. Even then, it might not explain what we think it does. The bottom line? Be careful when it comes to platoon splits and assign heavy doses of skepticism about small samples of solid or awful performance.

Eric Seidman is an author of Baseball Prospectus. 
Click here to see Eric's other articles. You can contact Eric by clicking here

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