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.