MLB Umpire Bias Calculator

While baseball data usually focuses on player matchups, the historical record between certain teams and umpires reveals staggering disparities. Across 4,641 team-umpire pairings, historical win rates swing by more than 40 percentage points from a team’s best umpire matchup to their worst.

For instance, the San Francisco Giants have won 41% more often with Jansen Visconti behind the plate than their franchise baseline, while the LA Angels’ win rate plummets 43% below average when Carlos Torres calls their games. Meanwhile, Vic Carapazza historically ejected Blue Jays personnel at a rate 25.7 points above the league average. These are the kinds of edges that move prediction markets like Kalshi and Polymarket, where game-level outcomes trade in real time.

We ranked MLB umpires since 1974 on strike zone accuracy, ejection rates, and run differentials. Search your team below.

The headline numbers

• The dataset covers 4,641 umpire-team pairings across 217 umpires and all 30 MLB teams (1974-2025).
• The gap between a team’s best and worst umpire pairing can exceed 40 percentage points in win probability.

Strike zone accuracy

• Rob Drake has the worst strike zone accuracy of any active umpire at 91.32%, across 1,396 games.
• John Libka leads all active umpires at 94.95% accuracy. Pat Hoberg, long considered the league’s gold standard, was fired by MLB in 2024 following a gambling investigation, leaving a clear gap at the top.

Umpire-team patterns that hold over large samples

• Mark Wegner has called 56 games involving the Cincinnati Reds. Their win rate drops 27 percentage points below baseline in those games.
• D.J. Reyburn is +0.27 for the Red Sox over 26 games, but separately appeared as one of the worst umpires for the Yankees.

The most umpire-sensitive team

• The Tampa Bay Rays have the widest variance of any franchise, with a standard deviation of 0.112 across 127 umpires. Their results swing harder based on who is behind the plate than any other team in the league.

Ejections

• Vic Carapazza historically ejected Blue Jays personnel at a rate 25.7 points above the league average, the highest team-specific disparity in the dataset among umpires with 20+ games.

Please scroll the calculator to get the full view of the data!