Similar to FIP, tRA uses a mathematical formula to isolate the pitcher from his defense.
The hitter may also hit a line drive, a ground ball, an outfield fly, a popup, a bunt or a home run.
These possibilities can be regarded as being governed by the pitcher, provided that there is a large enough sample size.
"[1] tRA uses play-by-play data gathered from each MLB season in order to give each possible outcome between a pitcher and a batter a linear weight.
Once these values are obtained, tRA can be converted to runs per nine innings by taking (xRuns/xOuts)*27.