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Wednesday, November 18, 2020

Pondering a First Inning Mystery

You’ve heard of home field advantage. It’s simply a part of sports, like gravity or Tom Brady being competent and obnoxious. Here’s a dirty little secret, though: A decent chunk of home field advantage is actually first-inning advantage. Here, take a look at how home and away batters performed in the first inning and thereafter from 2010 to ’19:

The first inning has the biggest gap, with only the fifth coming even close. It’s a consistent effect year-to-year, and it’s a big deal: A 22-point edge in wOBA works out to three-quarters of a run per game, which would work out to roughly a .570 winning percentage, significantly higher than the actual edge. If you could bottle that edge and apply it to every inning, baseball would look very different.

This isn’t some novel effect I’ve just discovered. It’s well-established, though I’ve never seen a completely satisfactory explanation for it. Could it be that the home team’s defensive turn in the top of the first warms them up for their turn at bat? Maybe! One counterpoint here: Home DHs have a 20-point wOBA advantage on away DHs in the first inning, then only a six-point advantage thereafter. Maybe it’s not that, then.

A theory that makes more sense to me is that home pitchers have a unique advantage in the first inning. In that inning, and that inning alone, they can exactly predict when they’ll be needed on the mound. Have a perfect warmup routine? You can finish it just before first pitch, then transition directly to the game. Visiting pitchers are at the mercy of the game. Start too late, and you won’t be ready in time for the bottom of the first. Start too early, and an extended turn at the plate might leave you cold.

RoyalsRetro (AG#1F) Posted: November 18, 2020 at 02:25 PM | 4 comment(s) Login to Bookmark
  Tags: home field advantage

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   1. Rally Posted: November 18, 2020 at 03:21 PM (#5989604)
I wonder if that held up for teams batting last in a road park, which we saw a few times in 2020.
   2. Kiko Sakata Posted: November 18, 2020 at 03:43 PM (#5989608)
Dave Smith gave presentations on this at back-to-back SABR conventions. His big find was that the home team's run-scoring advantage in the first inning was correlated to the length of the top of the first inning - the longer the top of the first, the more runs teams scored in the bottom of the first (so, your worst-case scenario for the road team is a long, drawn-out, but ultimately scoreless top of the first). The most reasonable sounding explanation I heard for this was that the visiting pitcher was adversely affected by having to sit down after his pre-game warmup and took a while to get acclimated. Following up on #1, one sub-theory of this was that the visiting pitcher was less comfortable with the pitcher's mound than the home pitcher (it being his home mound, of course).
   3. Walt Davis Posted: November 18, 2020 at 04:02 PM (#5989619)
His big find was that the home team's run-scoring advantage in the first inning was correlated to the length of the top of the first inning - the longer the top of the first, the more runs teams scored in the bottom of the first

As stated, that's not HFA. HFA is out-scoring the opponents. A long top 1st is more likely to be a top first with runs scored. That this might correlate with runs scored b1 might be any number of things -- good day for offense, 5th starters for both teams, whatever -- but surely runs scored in the top make it less likely the home team is ahead after one. That correlation doesn't sound like HFA, that sounds like "conditions are the same for both such that frequently both have long or both have short innings." HFA would be "the longer t1 then the more likely the 1st inning score gap is larger" ... which might be true for all I know. (More realistically just "the more likely the home team is ahead after 1.")

Based on intro, if it would be about 3/4 of a run over 9 innings then presumably about .08 per inning or 1 run every 12-13 home games or 6-7 runs over the full season.
   4. sunday silence (again) Posted: November 18, 2020 at 09:22 PM (#5989751)
Ive already mentioned this a few times before in citing a HFA study that was published a few years ago. The most reasonable explanation seems to be that HFA is linked to familiarity with surroundings. That sounds eminently reasonable.

that it exists mainly early in the game ties into that. As I recall that study also showed that the HFA in other sports also existed mainly in the early part of the game. And if Im also recalling correctly it was impactful in baseball at the beginning of a series rather than in game 3.

There doesnt seem to be much of a mystery although more research would certainly be better.

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