Friday, September 25, 2020
Run Values By Pitch Count
The typical way we think of run values is at the plate appearance level. This is something most of us learned through my saber-hero Pete Palmer in The Hidden Game of Baseball in the 1980s. The idea is that every base-out situation has a run potential. And after the event, the new base-out provides a new run potential. The CHANGE in those run potential is what we attribute to the event. A strikeout with bases empty and 0 outs for example turns the run expectancy from .481 runs to .254 runs. And so, the change in run expectancy, or the run value, of the strikeout is -0.227 runs. If the bases are loaded with one out, a strikeout has a run impact of a whopping -0.789 runs. So, the impact of the event is highly dependent on the circumstances.
We can go beyond the base-out situation though. We can include the inning and score. That's what Win Expectancy and Win Probability Added address.
We can go the other way, and in addition to the base-out, also include the ball-strike count. In other words, going from a 0-0 to a 0-1 count is good for the pitcher and bad for the batter. A called or swinging strike changes the run potential downwards. But we can go even further and combine the ball-strike count and the base-out situation. And so going from 0-0 to 0-1 with bases empty 0 outs has a run value of -0.04 runs. But doing so with bases loaded and 1 out is -0.14 runs. I posted this long overdue chart a couple of years ago. That shows the run expectancy of all 288 base-out-ball-strike states as well as the run values.
These run values is what you see on Savant, like on the Swing-Take Leaderboard.