Expanding the Strike Zone for Fun and Profit

Ask pretty much any major league hitter, and they’ll tell you that they earn their paycheck with runners in scoring position. A base hit means a run, and you have to score runs to win games. An out — particularly a strikeout — squanders an opportunity to score, and those come vanishingly rarely these days, what with every pitcher in baseball throwing 100 mph with a wipeout slider and all. It’s the highest-leverage spot you can hit in; succeed with runners in scoring position, and your team will probably win, but fail, and it’s going to be a long night.
As far as we can tell, success in those situations — runners in scoring position, high leverage, you name it — isn’t predictive of future success. But that doesn’t mean approach isn’t predictive of future approach, and as you might imagine, hitters behave differently when they can smell an RBI opportunity.
One easy way to conceptualize this change in approach is to think of the edges of the zone and the area just outside of the strike zone — the Shadow Zone, in Statcast parlance — as a good test of what a hitter wants to do. On pitches down the heart of the plate, swinging is a clear best choice. On pitches nowhere near the zone, taking is the only right choice. But pitches that could go either way? The best strategy depends on what you’re trying to accomplish.
With runners in scoring position and no one on first — in other words, a situation where a walk is far worse than a hit — major leaguers have swung at shadow zone pitches 56.4% of the time (in the last two years). On the whole, they’ve only swung 52.9% of the time at those pitches. In other words, they increase their borderline pitch swing rate by 3.5 percentage points when the gap between a walk and a single is the largest.
That’s a rather unimpressive number. It’s the clearest time to swing that you can imagine, and batters are hardly changing their behavior. But that’s logical, when you think about it. Walks aren’t suddenly worthless just because you could drive in a run; juicing up the bases for the next batter still has value. And swinging at borderline pitches is hardly the best way to drive in runs; taking borderline pitches and waiting for a mistake, or for the pitcher to challenge you, might be a better decision.
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