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Stat Questions: What’s Up With Those “vs Starter” Platoon Splits?

Posted by Neil on October 18, 2013

Here's another question I get pretty regularly when answering our bug reports: what's the deal with those "vs LH/RH Starter" platoon splits? To wit:

"How can Reed Johnson hit 32 HR's off of LH Starters when he hit 27 vs LHP?"

At a glance, it seems like we're saying "this is the player's stat line just against the opposing starter, broken down by that starter's handedness." In which case it would seem to be a bug when a guy has bigger totals against, say, lefty starters than against lefties in total.

Except that the definition I just wrote is not at all what that split is measuring. Instead, the "vs LH/RH Starter" split adds up all stats accumulated in games where the opposing starter was of a certain handedness, INCLUDING STATS ACCUMULATED LATER IN THE GAME WHEN THE STARTER IS PULLED, REGARDLESS OF THE RELIEF PITCHER(S)' HANDEDNESS.

Despite bolding, italicizing, and going all-caps, I still don't think I emphasized that enough. I realize the description of the split seems like it's talking only about stats accumulated against the starters, but it's really just counting up all stats in games where the opposing starter threw a certain way -- a BIG difference. If you want to know about performance against just starters of a given handedness... well, that's a double split, so we can't answer that right now. But we do hope to add the capacity for double splits in the future.

Anyway, now you might be saying, OK, well what's the point of that split, then? It seems pretty useless. And in some ways it is, for recent seasons at least -- but it's the only way we can approximate platoon splits for pre-PBP era players (1940s and before). Even going back to 1916, we at least know who started each game and their handedness, which usually is good enough to get platoon data on the majority of PAs (especially before managers started aggressively using relievers).

So that's why that split is there, even if it's not especially useful for 2013 players. And now you know what that split means, even if it seems like it should mean that other thing (which it DOESN'T).

This entry was posted on Friday, October 18th, 2013 at 3:56 pm and is filed under Announcement, Baseball-Reference.com, Stat Questions. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

3 Responses to “Stat Questions: What’s Up With Those “vs Starter” Platoon Splits?”

  1. Bring on the double splits! It's good to know what the "vs. Starter" split is for anyway.

  2. I agree with Gnomez. :)

  3. They are not at all useless nowadays. They can give you a better sense of the effective platoon difference between two players, if you don't expect to pinch-hit.

    In this WS, the Cardinals, a team that hit much less well against LHP, will be facing a LHP twice, while the Red Sox, a team that had a similar but milder split, will be facing all RHP. The way to estimate the effect of that on the series is to use the team splits in games started by RHP and LHP.

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