What is a Ball in Play in Baseball? Definition and Examples
A ball in play is any batted ball that lands in fair territory and is not a home run, strikeout, walk, or hit-by-pitch — the subset of plate appearances where fielders have a chance to record an out and batters rely on batted-ball luck.
What is a Ball in Play?
A ball in play (BIP) is a batted ball that is hit into fair territory and remains in the field of play, giving the defense an opportunity to record an out. It excludes home runs, strikeouts, walks, hit-by-pitches, and foul balls that are not caught. In sabermetrics, balls in play are the core of BABIP (batting average on balls in play) and are used to separate a hitter's skill from his batted-ball luck. Every time a batter puts a ball in play, the defense has a chance to make a play — and the outcome is partly random.
How It's Calculated and Measured
A ball in play is counted when the plate appearance ends with a batted ball that lands in fair territory and is not a home run. The formula:
BIP = Plate Appearances - Strikeouts - Walks - Hit-by-Pitches - Home Runs - Sacrifice Flies - Sacrifice Bunts
Statcast tracks balls in play with a binary flag: 1 if the ball is in fair territory and fieldable, 0 if it is a home run, foul out, or strikeout. The "in play" designation includes ground balls, line drives, pop-ups, and fly balls that stay in the park. A ball that is caught for an out is a ball in play. A ball that lands in the stands for a ground rule double is also a ball in play — it is fair and not a home run.
Worked Example: Real Player Numbers
In 2024, Los Angeles Dodgers shortstop Mookie Betts had 693 plate appearances. He struck out 91 times, walked 86 times, was hit by 3 pitches, and hit 19 home runs. His balls in play:
BIP = 693 - 91 - 86 - 3 - 19 - 4 (sac flies) = 490
Betts put 490 balls in play, and his BABIP was .316 — meaning he got a hit on 31.6% of those 490 balls. His overall batting average was .289, but his BABIP tells you that on balls in play, he was above the league-average .290 BABIP, which is typical for a hitter with his speed and line-drive rate.
For pitchers, balls in play matter too. In 2024, Seattle Mariners ace Logan Gilbert allowed a .262 BABIP — well below league average, which suggests some batted-ball luck. His FIP (Fielding Independent Pitching) was 3.76, higher than his 3.23 ERA, because FIP removes balls in play entirely and focuses on strikeouts, walks, and home runs.
Why It Matters
Balls in play are the dividing line between pitcher-controlled outcomes and defense-controlled outcomes. Strikeouts, walks, and home runs are "three true outcomes" — they happen without fielders. Balls in play involve the defense, the ballpark, and random variation. For fantasy players, a hitter with a high BABIP on balls in play may be due for regression; a pitcher with a low BABIP may be overperforming.
For front offices, balls in play drive defensive evaluation. A pitcher who induces weak contact — soft ground balls and pop-ups — will have a lower BABIP than one who gives up hard line drives. Statcast's expected batting average (xBA) uses exit velocity and launch angle on balls in play to estimate what a hitter "should" have hit, separating skill from luck.
Limitations and Common Misconceptions
The biggest misconception: all balls in play are created equal. A 110 mph line drive and a 60 mph dribbler are both balls in play, but their outcomes are wildly different. BABIP does not account for quality of contact — that is why xBA and xwOBA exist. Another misconception: balls in play are purely luck. Hitters with elite speed beat out ground balls, and hitters with high launch angles turn fly balls into extra-base hits. Balls in play are a mix of skill and randomness.
A ball in play is not the same as a "ball hit in the air." A pop-up to the catcher is a ball in play. A foul ball caught for an out is not a ball in play — it is a foul out, which does not count toward BABIP. Sacrifice flies are balls in play for the batter but are excluded from BABIP because they do not count as at-bats.
Related Terms
In Legends Deck
Legends Deck simulates every batted ball as a ball in play unless it leaves the yard. The sim uses each batter's exit velocity, launch angle, and sprint speed to generate a batted-ball distribution — ground balls, line drives, pop-ups, and fly balls — then rolls against the fielder's range and arm to determine the outcome. A card with high "contact" and "speed" ratings will turn more balls in play into hits, while a pitcher card with high "ground ball" and "soft contact" ratings will suppress BABIP and strand runners.