Alan Porter

What we can't say about Alan Porter

This season is 3,646 graded takes, which puts Alan Porter's overall accuracy at 92.9% ± 0.8 (95% interval). That is a real measurement against a league spanning about four points end to end. It is not enough for anything finer, and here is the arithmetic rather than our word for it:

• how the zone moves with two strikes — about 729 takes, so ±1.9 points. (the league-wide two-strike effect is about 1 point in 2026.)
• any single corner of the zone — about 304 takes, so ±2.9 points. (corner cells are where umpires actually differ.)
• whether one pitcher is called tighter than another — about 61 takes, so ±6.4 points. (a given pitcher is worked once or twice a season.)

And a note on the number itself: an accuracy figure is a rate plus a convention for what counts as a miss. Ours grades every taken pitch against the rulebook zone as the feed reports it. Others are more forgiving — UmpScorecards counts a call wrong only when the pitch was at least 90% likely to be a strike — so two sites can print the same percentage about the same umpire and not mean the same thing by it. How the grade is built.

The overturn rate is a different kind of number and does not belong beside the grade: it is accuracy on the 116 pitches players chose to challenge, which are the pitches they already believed were wrong. 116 is enough to print it with its own denominator, which is what we do — but it still ranks umpires by how often they are appealed, not by how often they are right.