Breaking Down Plate Discipline by Pitch Type

By ANDREW KYNE

Last week, I presented a way to visualize plate discipline, referencing some of the numbers on FanGraphs like O-Swing% and Z-Swing% that make use of Baseball Info Solutions’ pitch charting data.

For each player, those plate discipline metrics obviously come at an aggregated level across pitch types. When we see that Joey Votto swung at 16 percent of pitches thrown outside the strike zone last year, that’s his total performance — against fastballs, curveballs, sliders, changeups, etc.

But what if we split those out? What kind of discipline does Votto — and the rest of the league — have against different types of pitches?

Let’s consider the chase rates — the percentage of swings taken on pitches outside the zone (O-Swing%) — for the 179 batters who saw at least 1,000 total pitches out of the zone in 2018. For now, let’s just break it down by O-Swing% on fastballs and O-Swing% on breaking balls (curves and sliders).

Here’s a look at the leaderboard for each:

And here’s the correlation between those two metrics for these players:

And some takeaways:

— There’s a positive relationship, which is expected — batters who chase (or don’t chase) fastballs probably also chase (or don’t chase) a lot of breaking balls.

— However, the rate of chasing breaking balls is, understandably, higher. Using the trend line on the graph, note that a 20 percent fastball O-Swing% corresponds with something more like a 26 percent breaking ball O-Swing%, on average.

— Overall, the batters in this sample swung at out-of-zone fastballs 27 percent of the time, compared to 33 percent for out-of-zone breaking balls.

— Of the 179 batters, 29 had a lower O-Swing% against breaking balls than against fastballs. Three notables are those labeled on the graph: Votto, Juan Soto, and Jose Ramirez. All three showed excellent discipline against all pitch types, but were particularly impressive against breaking balls. And all three are great offensively.

— On the other side of that is Yasmani Grandal. Overall, he had a very good O-Swing% at 23 percent. But he was outstanding against fastballs (14 percent), and only about average against breaking balls (33 percent). Last season, he hit .279 with a 1.046 OPS in at-bats ending with a fastball, but only .210 with a .555 OPS in at-bats ending with a slider or curveball.

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