MLB Ump Watch
The 2025 Ump Run-Factor Board: Overs, Unders, and the Men in Blue
Published
Every home-plate umpire carries his own strike zone, and over enough games that zone becomes a run environment you can measure. From our Retrosheet archive, these are the rolling three-season run factors through 2025, where 1.00 means dead-league-average.
There are 73 qualified names in the sample, spanning about 12 percent above average down to 14 percent below, a wider spread than most fans would guess.
Friendly skies for hitters
Mark Wegner owns the most hitter-friendly environment in the sample: a 1.125 run factor across 71 games behind the plate, where scoring has run about 12 percent above the league norm.
Next in line: Adrian Johnson, 1.101 across 89 games.
Next in line: Dan Bellino, 1.097 across 96 games.
The tight zones
At the other extreme, Brennan Miller has squeezed scoring hardest: a 0.863 factor over 73 games, where scoring has run about 14 percent below the league norm.
David Rackley is nearly as stingy at 0.893 over 92 games.
By the numbers
Here are the top five run environments, highest factor first:
| Umpire | Run factor | Games |
|---|---|---|
| Mark Wegner | 1.125 | 71 |
| Adrian Johnson | 1.101 | 89 |
| Dan Bellino | 1.097 | 96 |
| Mike Muchlinski | 1.093 | 86 |
| Chris Guccione | 1.091 | 79 |
Worth remembering
Because every factor rides a rolling three-season window, the board moves slowly and honestly: no single series, however strange, can rewrite it.
Think of it as weather: nobody controls it, everybody plays in it, and only some people bother to check it before first pitch.
These are historical tendencies from seasons past, not tonight's assignments, treat them as trivia about the shape of the sport, not a betting signal on any specific game.