How the Strike Zone Alters by Count
Everyone knows the strike zone alters based off the count. It shouldn’t, but umpires can’t help but be biased. If the count is 3-0, the strike zone will be more forgiving to the pitcher. If the count is 0-2, the zone will be more forgiving to the hitter. What does the zone look like for each possible count? Using Statcast detailed zones, let’s look at the called-strike rate on the corners for the last five years.
| Count | Called Strike % |
|---|---|
| 0-0 | 25.90% |
| 0-1 | 15.47% |
| 0-2 | 9.40% |
| 1-0 | 27.48% |
| 1-1 | 19.38% |
| 1-2 | 11.70% |
| 2-0 | 30.72% |
| 2-1 | 23.27% |
| 2-2 | 15.56% |
| 3-0 | 35.86% |
| 3-1 | 24.64% |
| 3-2 | 16.59% |
As expected, the lowest rate comes from 0-2 counts, and the highest rate comes from 3-0 counts. But the difference is shocking. A pitch in the same location is called a strike 26.46% more often, just because of the count. Here is the same table, ordered by increasing rate.
| Count | Called Strike % |
|---|---|
| 0-2 | 9.40% |
| 1-2 | 11.70% |
| 0-1 | 15.47% |
| 2-2 | 15.56% |
| 3-2 | 16.59% |
| 1-1 | 19.38% |
| 2-1 | 23.27% |
| 3-1 | 24.64% |
| 0-0 | 25.90% |
| 1-0 | 27.48% |
| 2-0 | 30.72% |
| 3-0 | 35.86% |
Four of the first five are two-strike counts, where umpires seem to favor the batter. The average rate in those zones in the past five years, regardless of count, is 22.45%. The rate on all two-strike counts is 13.16%, a good bit below the overall average. Hitters ahead in the count have nearly twice as many strikes called on them in the corner zone, as the rate spikes from 13.68% when they are behind to 25.99%.
What stands out is how much one strike can affect the umpire. The last four are all no-strike counts, and there is an over 10% difference between 3-1 and 3-0. One strike significantly changes how the zone is called. Balls, on the other hand, do not have the same effect on the zone. Two-ball and three-ball counts are up and down the list. The amount of strikes controls the way the zone is called.
It’s a given that the zone will expand to favor pitchers when they are behind, but the difference is surprising. A first-pitch strike is always preferred, but pitchers also get a significant amount of leeway as they fall behind.
Why, if the technology exists, do we not go to the automated computer strike zone we see each and every game?
Really interesting work! However, I think it would be prudent to look into swing rates on these counts as well. Some of this result may be driven by batters shouldering their bats for 3-0 counts, thereby increasing the likelihood of a called strike.
Calling a strike to punish a batter for “shouldering” is even more absurd than coercing full counts by expanding and contracting the zone depending on the count.