What is OPS Against? Definition, Formula, and Example
OPS against (OPSA) measures the on-base plus slugging percentage that opposing hitters produce against a pitcher — the single best quick gauge of how thoroughly a pitcher suppresses offense.
What is OPS Against in Baseball?
OPS against is the on-base plus slugging line posted by all batters facing a given pitcher. Where batting average against only tracks hits, OPS against captures everything a pitcher allows: walks, hit batters, singles, and extra-base damage. A pitcher with a .600 OPS against is turning every hitter he faces into a below-average bench bat; a pitcher at .800 is being treated like a batting-practice arm.
How It's Calculated
OPS against combines two components computed from the pitcher's perspective:
- OBP against = (H + BB + HBP) / (AB + BB + HBP + SF)
- SLG against = Total bases allowed / At-bats against
- OPS against = OBP against + SLG against
All plate appearances against the pitcher are aggregated for the season. League-average OPS against typically sits near .710-.730, mirroring overall league OPS. Statcast-based variants like xwOBA against replace outcomes with quality-of-contact expectations.
A Worked Example
In his 2020 Cy Young season, Shane Bieber held opposing hitters to a .167/.240/.369 line — an OPS against of .609 across 77.1 innings. Deconstruct it: hitters reached base at just a .240 clip and slugged like light-hitting shortstops. Compare that to a replacement-level arm allowing an .820 OPS against — roughly what every hitter produced against the worst qualified starters in 2023. The 200-point gap between Bieber and a struggling starter, spread over 800 batters faced, is the difference between an ace and a DFA candidate.
Why It Matters
OPS against is the pitching mirror of the most popular hitting stat, which makes it instantly interpretable. Front offices use it in arbitration hearings and trade evaluations because it bundles contact management and free-pass prevention into one number. It's especially useful for relievers, whose small inning totals make ERA volatile — a closer with a .520 OPS against is dominant even if one inherited-run meltdown wrecked his ERA. Fantasy players use it to find buy-low starters whose ERA is inflated by sequencing luck.
Limitations and Misconceptions
OPS against is context-blind: it ignores park factors, defense, and opponent quality. A Rockies starter's OPS against is inflated by Coors Field; that's what ERA+-style adjustments or xwOBA against are for. It also treats a walk and a single as partially equivalent through the OBP/SLG blend, which slightly undervalues on-base suppression. And it is not the same as WHIP — WHIP counts baserunners per inning but ignores how far those runners hit the ball.
Related Terms
In Legends Deck: Pitcher cards are tuned so that simulated OPS against tracks each hurler's real Statcast profile — command, stuff, and contact suppression all feed into how opposing lineups perform against your rotation.