Los Angeles Dodgers

Expected runs subtracted is a better metric than ERA because it isolates the pitcher by taking relievers out of the equation. Let's take a look at two examples:

Example 1. Two starting pitchers A and B each load the bases with no outs, then exit. Reliever A comes in and retires the side with no runs; Reliever B allows all three to score. Starter A gets 0 earned runs charged, and Starter B gets 3 runs charged to his ERA, even though they both left in the same situation. But under runs expectancy, both starters are charged the same −1.938 runs (end state 0.498 − start state 2.436), regardless of what the reliever does.

Example 2. Reliever C enters at the start of an inning with no outs and a clean base path, then retires the side: runs subtracted = 0 − 0.498 = −0.498. Reliever A (from Example 1) entered with bases loaded and no outs and stranded all three: runs subtracted = 0 − 2.436 = −2.436. Both pitched one inning, allowed zero runs, and carry the same ERA impact — but runs expectancy subtracted properly credits Reliever A with the much harder task.