Expected stats (the x stands for expected) are one of Statcast’s biggest contributions. Instead of looking at the actual result, they estimate what should have happened based on the quality of contact: how hard and at what angle the ball came off the bat. The most widely used are xwOBA, xBA (expected batting average) and xERA.
How do they work?
Statcast measures every batted ball and, using thousands of historical cases, calculates the probability that type of contact becomes a hit. If a hitter smokes a lot of hard line drives that, through bad luck, get caught, his real average will be low but his xBA high: a sign he «deserved» more.
How do you read them?
- Actual result below expected: bad luck; likely to bounce back.
- Actual result above expected: good luck; likely to cool off.
Examples
- A hitter batting .250 but with a .290 xBA is hitting the ball better than his line suggests: a candidate to improve.
[Live data — Statcast] Biggest gaps between actual and expected results this season: (filled in automatically).
Why they matter
Expected stats separate skill from luck using the physical data of the batted ball, not the randomness of where it landed. They’re the most modern tool for predicting who is about to rise or fall.
Related stats
Frequently asked questions
What does the «x» mean?
It comes from expected: the value the quality of contact suggests, not the actual result.
Where does this data come from?
From Statcast, the camera and radar system that measures every batted ball and pitch.
