Unpacking the Impact of Foul Balls on Strikeouts
In eight of the 12 different count-states, fouls and whiffs come with the same penalty: a strike. In a 1–1 count, for example, it really doesn’t matter whether you look silly swinging and missing at a curveball or just miss a home run by being a few inches wide of the foul pole. In either case, hitters have to come back for another swing, with the count now 1–2.
We all know this. Those are just the rules of the game. But it creates a very interesting hierarchy for hitters. When a hitter swings, only one of three things can happen: He can put the ball in play, foul it off, or whiff. And, as mentioned, for two-thirds of those outcomes — the foul and the whiff — no distinction is even made in eight of the 12 count-states. No wonder that the league-average hitter, by run value, is penalized when he swings.
But fouls have a unique property that makes them wholly different than whiffs: the ability to prolong at-bats. In the same way that you can’t lose on a serve in ping pong, you can’t strike out on a foul ball (bunts excluded). While they carry the same penalty as whiffs in all non–two-strike counts, foul balls manage to be the only safety net for hitters when their backs are against the wall, and to me, it makes for a pretty interesting dichotomy when you break it down that way.
Because foul balls provide this special safety net for hitters, it would make sense intuitively that hitters who foul off more pitches probably strike out less. If a hitter fouls off a lot of pitches, especially relative to the number of whiffs he creates, he is almost certainly going to avoid a K and eventually should get a pitch to put in play. Indeed, there is a pretty strong correlation between foul-to-whiff ratio and strikeout rate: