FanPost

New Proposed Stat: Isolated ERA (iERA)

This is a concept I've been thinking about for a while, and I think I came up with a good formula for how to calculate it. I'd like to run the stats for the Royals and see the results, but I need help finding some of the data needed to calculate it - see the questions at the bottom for details. Would appreciate any help finding this data, and welcome any feedback. Without further ado, I give you...

Isolated ERA (iERA)

The goal of Isolated ERA (iERA) is to eliminate the effects of the rest of a pitching staff on an individual pitcher’s ERA. When a pitcher leaves runners on base that they are "responsible for", whether or not the next pitcher(s) allows these runners to score no longer influences the original pitcher’s ERA. Their iERA is adjusted based on league average performance for how likely these runners score. Similarly, relief pitchers are credited for inherited runners they prevent from scoring, but still held partially responsible if allowing them to score (again adjusted for performance compared to league average).

Calculation:

( ERp + ARe - ARi ) / IP * 9

ERp = Earned Runs scored while pitcher was in the game, regardless of whom the runs were "charged to" using traditional ERA scoring method.

ARe – League Average Runs scored by the baserunners left for specific scenario (bases occupied and number of outs) when pitcher Exits game. Scenario should exclude unearned baserunners or advancements.

  • Example 1) Pitcher A exits with 2 outs and man on 1st. League Average is this runner scores 0.12 runs on average. Thus 0.12 runs are added for Pitcher A – regardless of whether this runner actually scores or not.
  • Example 2) Pitcher B exits with 0 outs and bases loaded. League average is that these 3 base runners score 1.78 runs on average. Thus 1.78 runs are added for Pitcher B – regardless of whether any of these runners actually score.

ARi – League Average Runs scored by the baserunners left for specific scenario (bases occupied and number of outs) that pitcher Inherits when entering game

  • Example 1) Pitcher A enters with 2 outs and man on 1st. League Average is this runner scores 0.12 runs on average. Thus 0.12 runs are subtracted for Pitcher A when he enters game, regardless of whether this runner scores.
  • Example 2) Pitcher B enters with 0 outs and bases loaded. League average is that these 3 base runners score 1.78 runs on average. Thus 1.78 runs are subtracted for Pitcher B when he enters the game – regardless of whether any of these runners actually score.

Examples for individual outings:

  • Pitcher A pitches 6.2 innings, gives up 3 earned runs, and exits with 2 outs and man on 1st. League average is runner on 1st with 2 outs scores average of 0.12 runs.
    • Pitcher A’s iERA = (3 + 0.12 – 0) / 6.67 * 9 = 4.21 iERA
  • Pitcher B enters game with 2 outs and man on 1st. League average is runner on 1st with 2 outs scores average of 0.12 runs. Pitcher B gives up 2 run HR and then retires next batter.
    • Pitcher B’s iERA = (2 + 0 – 0.12) / 0.33 * 9 = 50.76 iERA
  • Pitcher B enters game with 2 outs and man on 1st. League average is runner on 1st with 2 outs scores average of 0.12 runs. Pitcher B retires next batter to end inning.
    • Pitcher B’s iERA = (0 + 0 – 0.12) / 0.33 * 9 = -3.24 iERA (negative iERA due to reducing expected runs)
  • Pitcher B enters game with 1 outs and man on 1st. League average is runner on 1st with 1 out scores average of 0.24 runs. Pitcher B gets an out, walks next batter and then exits with runners on 1st and 2nd. League average is runners on 1st and 2nd with 2 outs score average of 0.34 runs.
    • Pitcher B’s iERA = (0 + 0.34 – 0.24) / 0.33 * 9 = 2.70 iERA

Open Questions:

  • To calculate ARe and ARi, I’m using Baseball Prospectus’s Run Expectations. However, since I believe this calculates the total runs expected for the inning, and not the runs expected to be scored just by the runners on base – I’m subtracting the expected runs for bases empty. However, I can only find these numbers for MLB overall – are these available by league anywhere?
  • I can’t find the game scenarios for when pitchers enter/exit games – is this available anywhere? I’d like to calculate the iERA for the Royals staff, but I can’t without this data. I’m sure it has to be available somewhere, so would appreciate if someone can point me in the right direction.

This FanPost was written by a member of the Royals Review community. It does not necessarily reflect the views of the editors and writers of this site.

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