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MLB replay review can change certain eligible calls on plays such as force outs, catches, home runs and baserunning decisions. The Automated Ball-Strike (ABS) Challenge System has a narrower role: starting in 2026, it can change only the plate umpire’s called ball or strike when the batter, pitcher or catcher immediately challenges it. The umpire still makes the initial pitch call; ABS does not automatically call every pitch.
At a glance: two different kinds of review
| Question | MLB replay review | ABS Challenge System |
|---|---|---|
| What can be challenged? | Calls in MLB’s defined reviewable categories, including specified boundary, force-play, catch and baserunning calls. | Only the home-plate umpire’s called ball or strike on a pitch. |
| Who can initiate it? | A manager may challenge; the crew chief may initiate review under specified authority. | The batter, pitcher or catcher involved in the pitch, by an immediate cap or helmet tap. |
| Who decides? | Full-time MLB umpires at the Replay Command Center. | Hawk-Eye pitch tracking compares the pitch with the ABS zone; the outcome is relayed and displayed. |
| What can change? | A reviewable call and, when needed, runner placement to reconstruct the proper result. | The ball-or-strike ruling; related play consequences are handled according to what the original call affected. |
| How is a change decided? | Replay officials need clear and convincing evidence to change the call; otherwise it may be confirmed or allowed to stand. | The tracked pitch location is compared with the system’s defined strike zone. |
What MLB replay review can change
Replay review is for an enumerated set of disputed calls, not every close play. A manager challenge or a crew-chief review sends an eligible play to the Replay Command Center. MLB says replay officials are expected to decide within two minutes, with some exceptions; their decision is final and cannot be reviewed again. See MLB’s replay review rules.
Home runs, boundaries and fair-or-foul calls
- Potential home-run questions, including whether the ball left the field, hit a fence or object, involved fan interference, or was fair or foul.
- Specified non-home-run boundary calls, such as a live ball bouncing out of play, hitting an obstacle, being caught near a boundary, or becoming dead after leaving the field.
- Fair-or-foul calls only when the ball first lands at or beyond the first- or third-base umpire’s set position.
Force plays, tags and catches
- Whether a fielder touched a base or tagged a runner, and whether the runner acquired the base.
- Whether an outfield fly ball or line drive was caught. Infield catches are not reviewable under this category.
Baserunning and other specified plays
- Whether a runner passed a preceding runner, scored before a third out, or touched a base.
- Certain collisions at home plate, tag-up calls, runner placement after a boundary call, and interference on double plays.
- Whether a pitched ball hit a batter, the batter’s clothing, or the bat. Replay cannot determine whether the pitch was in the strike zone when it hit the batter or whether the batter tried to avoid it.
What the ABS Challenge System can change
ABS challenges apply only to the plate umpire’s initial ball-or-strike call. The batter, pitcher or catcher involved must request the challenge immediately with a cap or helmet tap. Coaches, teammates and the dugout cannot prompt or make the challenge for them. The system then uses Hawk-Eye tracking to compare the pitch with the ABS zone; MLB says the result is relayed and displayed to ballpark spectators and broadcast viewers. MLB describes the system in its 2026 ABS explainer.
How MLB defines the ABS strike zone
The zone is a two-dimensional rectangle measured at the midpoint of home plate. It is 17 inches wide, matching the plate. Its top is 53.5% of the hitter’s measured height and its bottom is 27%. A pitch is a strike if any part of the ball touches any part of the rectangle. MLB says twelve Hawk-Eye cameras track pitches.
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Who gets challenges and when
Each team starts with two challenges and retains a challenge when successful. A team entering an extra inning with none receives one for that inning. Challenges are still subject to situations in which MLB rules prohibit them; a position player pitching is one such situation. The system is a player-initiated appeal of a particular pitch call, not automatic ball-and-strike officiating.
How the systems interact
ABS and replay review remain distinct procedures, but MLB specifies how they interact. An ABS challenge cannot be made after replay review; if both are requested simultaneously, the ABS challenge is accepted first. MLB’s rules also say the umpiring crew preserves calls unaffected by the challenged ball-or-strike ruling and adjusts only the affected result.
For example, if a runner steals third during a pitch that is challenged from ball to strike three, the runner can remain safe at third while the batter is retired. If a dropped pitch is overturned to strike three, the batter is out without the usual tag or force at first. These examples show why changing a pitch call does not necessarily erase every event that occurred on the play. See MLB’s ABS rules and examples.
Do not treat a hit-by-pitch review as a way to appeal the strike-zone judgment: MLB expressly excludes whether the pitch was in the zone when it hit the batter. The rules sources describe ABS as the avenue for challenging a called ball or strike; they do not establish replay review as a separate way to reverse an ordinary ball-or-strike call.
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What the 2025 ABS test figures do—and do not—show
MLB’s 2025 Spring Training test across 288 games averaged 4.1 challenges per game, with each challenge taking 13.8 seconds. MLB reported that 52.2% of challenged calls were overturned and that 2.6% of called pitches were challenged. In that test, pitchers and catchers had a 54.4% challenge success rate and hitters had a 50.0% rate. These are Spring Training trial results, not established 2026 regular-season rates. The figures are in MLB’s ABS explainer.
MLB’s 2025 Spring Training testing tracked 88,534 pitches, with four unavailable because of tracking glitches. MLB also reported that, in 2-2 counts, the umpire-called zone measured 449 square inches compared with 443 square inches for the ABS zone. MLB presents a slight expected reduction in strikeouts and increase in walks as expectations based on testing, not as measured 2026 outcomes.
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Which system applies to a disputed call?
- A disputed pitch call: an eligible player may immediately challenge the plate umpire’s called ball or strike through ABS, subject to its restrictions.
- A disputed play result: check whether the call falls within MLB’s defined replay-review categories and whether a manager challenge or crew-chief review is available.
- A pitch that hit a batter: replay may address whether contact occurred, but not whether the pitch was in the strike zone at contact or whether the batter attempted to avoid it.
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