Sunday, March 31, 2024
Extra Innings: whatsup?
Home win% in regulation games is 54%, but falls to 52% in extra innings for totally normal reasons, having nothing at all to do with who bats first or last.
This chart shows the win% season by season since 1969. I've included the Random Variation lines, which I have nominally set at 2 standard deviations. This implies we should expect to see 5% of these 55 data points (aka 3) to land outside these two lines. We see alot more than that. Why, I don't know. I used a flat 52% expected win%, and maybe it should be 51.5% one year and 52.5% another year. I'll leave that to the aspiring saberists. (click to embiggen)
Of course, the most striking thing in the chart is what's happened since 2020, with the extra inning placed runner (XIPR). Though inconveniently, the pattern started the season prior to that. Anyway, here's how it looks when we group in chunks of five seasons. The data point for "2010" you see at the bottom refers to seasons "2010 - 2014". And "2015" is "2015 - 2019".
We should only see, maybe, one point outside the 2SD lines, but we see three, with the one from 2020-present way outside even this standard. Something is definitely going on with how teams are approaching playing with the XIPR. I'm sure an aspiring saberist can look into this. Are there any teams that have figured it out? I'll leave that up to y'all to show.