Win Probability Changes

You may have noticed the Win Probability numbers have changed slightly. Don’t panic! There have been a few changes, for the better.

First off, we’re now using Tangotiger’s updated win expectancy tables which are no longer a flat 5.0 Runs per Game environment. Instead, we’re using the home team’s league, average run environment. This now puts batters and pitchers on “equal footing” and you should now be able to accurately compare batters and pitchers using WPA.

Second of all, we’re also using Tangotiger’s run expectancy tables to calculate Batting Runs Above Average (BRAA) for both batters and pitchers. Once again the run environment is set at the home team’s league, average run environment.

Next to BRAA there is a column titled “REW”, which stands for Run Expectancy Wins. This is a replacement for OPS Wins because we no longer need to estimate wins in a context neutral environment since we’re now using run expectancy.

Finally, Clutchiness has been shortened to Clutch (Clutchiness was excessively long) and is calculated as WPA/LI – REW.

Update (3/4/2007): Clutch has been switched back to being calculated with OPS Wins. More on this later.

Typically players remain in the same order, but their values have changed slightly. Batters should be slightly more valuable and pitchers slightly less valuable based on WPA scores.

We hoped you liked reading Win Probability Changes by David Appelman!

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REW: note that this does include “clutch” with respect to men on base. To exagerrate for illustration, say you have someone who hits .000 with bases empty and .500 with men on base. His REW will be much higher than someone who hit .500 with bases empty and .000 with men on base.

Therefore, the “clutch” portion only distinguishes between the timing in terms of inning and score, and does not also include the men on base clutch portion.

You could start with Linear Weights Wins (LWW I guess), and then have REW, and the difference would be his clutchiness based only on the base/out. Then the gap between REW and WPA is his clutchness base on the inning/score. WPA minus LWW is his overall clutch.

Jeter’s Clutch score dropped alot (used to be +2.5 wins and now he’s below 1.0 wins). My guess is that he performed great with men on base, and performed a bit better with the game on the line.

If you look at his performance with men on base and bases empty:

You will see it bears that out.

(There is an extra technicality with using the LI as well, but not important right now.)