Four Kinds of Zone

The Two Things That Matter

Every home plate umpire in MLB has a zone. It's not the rulebook zone and it's not the ABS zone — it's their zone, shaped by years of calling pitches and reinforced by muscle memory.

We classified every called pitch from the 2025 season — 380,000 pitches across 83 umpires with 10 or more games — against the ABS zone model. Two dimensions capture most of the variation between umpires:

1. Accuracy: How often do they get the call right? Range: 90.1% to 94.6% (a 4.5 percentage-point spread).
2. Borderline Strike Rate (BSR): On pitches within 1 inch of the zone edge, what percentage do they call as strikes? Range: 31% to 52% (a 21-point spread).

These two axes are essentially independent (r = -0.04). You can be accurate with any zone shape. That independence creates four natural quadrants — not discovered clusters, but descriptive bins that capture genuinely different umpiring styles.

The Scatter Plot

Each dot is an umpire. X-axis: how aggressively they call borderline pitches as strikes. Y-axis: how often they're correct. Dashed lines are median splits (accuracy 92.5%, BSR 42.7%). Labeled dots are notable umpires discussed below.

The Four Quadrants

Aggressive Ace (23 umpires)

High accuracy AND a wide borderline zone. These umpires call more borderline pitches as strikes and get the calls right. Pitchers love this assignment — the zone is generous and consistent.

Archetype: Edwin Jimenez (94.6% accuracy, 43% BSR, 7.7 wrong calls/game). The most accurate umpire in MLB who also calls an aggressive zone.

Conservative Ace (19 umpires)

High accuracy but a tight borderline zone. These umpires let borderline pitches go as balls more often — they'd rather miss a borderline strike than call a false one. Batters get more favorable counts.

Archetype: Derek Thomas (94.0%, 36% BSR). Tight but correct. Willie Traynor (93.2%, 32% BSR) is the most extreme — only 26% of his wrong calls are false strikes.

Wild Expander (20 umpires)

Aggressive zone but lower accuracy. These umpires call lots of borderline pitches as strikes but make more mistakes doing it. Pitchers get the wide zone but at the cost of inconsistency.

Archetype: Vic Carapazza (52% BSR — the highest in MLB, 92.4% accuracy). Ron Kulpa (49% BSR, 55% false strike rate — the only umpire whose wrong calls are mostly strikes called out of the zone).

Tight Struggler (21 umpires)

Conservative zone AND lower accuracy. These umpires miss more pitches that should be strikes — letting borderline calls go as balls when they shouldn't — while also not being more accurate overall. The toughest assignment for pitchers.

Archetype: Bruce Dreckman (90.1% accuracy — the lowest in MLB, 14.4 wrong calls/game). CB Bucknor (91.0%, a name familiar to any baseball fan).

The Profiles

What the Range Means in Practice

The 21-point BSR range is the most actionable finding. A pitcher facing James Jean (31% BSR) gets roughly 21 fewer borderline strike calls per 100 borderline pitches compared to Vic Carapazza (52% BSR). Over a full game with ~30 borderline pitches, that's about 6 extra balls — enough to meaningfully change pitch sequencing, walk rates, and game outcomes.

The accuracy range matters too: Bruce Dreckman makes 14.4 wrong calls per game vs. Edwin Jimenez's 7.7. That's nearly double the error rate — roughly 7 extra wrong calls per game.

The Bigger Pattern: Umpires Are Conservative

65% of umpires (54 of 83) have a false strike percentage below 45% — meaning when they miss, they miss by letting borderline pitches go as balls rather than calling them as strikes. The human zone differs from the ABS zone: umpires are generally more conservative, particularly at the vertical boundaries.

This has implications for the ABS challenge system in 2026. If umpires are naturally conservative, catchers — who see the pitch trajectory and have framing instincts — may have a structural advantage in knowing which pitches the umpire called incorrectly as balls. Our ABS challenge analysis found exactly this: the fielder side wins challenges at a higher rate (59.5% vs 49.8%).

Early 2026: Are Patterns Holding?

We have 10 umpires with 3+ games in the 2026 ABS era. Every single one improved their accuracy compared to 2025 — the mean jumped from 92.0% to 94.6% (+2.6 percentage points). Whether this reflects the ABS accountability effect or small-sample noise (3 games per umpire) is too early to say. We're tracking this as the season progresses.

What We Can't Say

• These quadrants are editorial bins based on median splits, not discovered clusters. A different split point would shift individual assignments.
• BSR and False Strike % are tightly correlated (r = 0.84) — they measure the same underlying "zone expansion" dimension, not independent traits.
• The 2025 patterns may not persist into 2026. The ABS challenge system may change umpire behavior.
• We cannot yet link zone style to game outcomes (wins, run scoring) without a much larger analysis.