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:
| Inning | Away | Home | HFA |
|---|---|---|---|
| 1 | .318 | .340 | .022 |
| 2 | .304 | .314 | .010 |
| 3 | .311 | .322 | .011 |
| 4 | .323 | .330 | .007 |
| 5 | .314 | .330 | .016 |
| 6 | .319 | .329 | .010 |
| 7 | .308 | .317 | .009 |
| 8 | .302 | .308 | .006 |
| 9+ | .296 | .297 | .001 |
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. Read the rest of this entry »
Jay Jaffe


