Reference
MLB analytics glossary
Every metric this API returns, with the formula, what it is for, and the specific way people get it wrong. Written from how these are actually computed here, not paraphrased.
The runs a plate appearance added or cost: the change in run expectancy for the base-out state, plus any runs that scored.
The average number of runs a team scores from a given base-out state to the end of the inning.
The number of outs and which bases are occupied: the situation a plate appearance starts in.
On-base percentage plus slugging percentage: how often a hitter reaches and how much damage the hits do, in one number.
Strikeouts as a share of plate appearances; walk rate is the same for walks.
Swinging strikes as a share of swings: how often a pitch makes hitters miss when they go after it.
What a pitcher throws and how often: each pitch type's share, velocity and results.
Where a hitter's balls in play go, as points on the field, with their trajectory.
Whether a ball in play was a ground ball, a line drive, a fly ball or a pop-up.
The win percentage a team's runs scored and allowed predict, which says how much of its record was luck in close games.
Our running team strength number: up after a win, down after a loss, by more when the result was a surprise.
The home team's chance of winning after each plate appearance, as ESPN computes it, from 2019.
The win chance a moneyline implies, with the book's margin still in it.
A sportsbook's last price before first pitch, the market's final word on the game.
How a game's price changed between opening and first pitch.
Baseball's point spread: almost always a run and a half, with the price doing the work.