Best lefty off all time? My vote is Koufax!

[Snowman]

Originally Posted by earlywynnfan

Back to the original Grove vs. Koufax line, can you please use your statistics to explain Koufax's widely disparate home vs. away records??

His away numbers are worse, for sure, but I don't know that I'd call them "widely disparate". There's an expected disparity for all pitchers when pitching at home and on the road. Part of the "home field advantage" in baseball comes from an umpire's subconscious bias in calling balls and strikes, just like in basketball with fouls. Even when they are trying their best to be neutral, it is somehow still human nature to call the games more favorably for the home team than the away team. The effect is small, but measurable over the course of a career. When you look at Koufax's career Home vs Away numbers, they don't really look all that out of line to me when you consider the fact that he pitched in a pitcher's park. Here's what I see. Note he had almost identical IPs for both. Also, ERA values are much more reliable over the course of a career with 1,000+ IP, so it's fair to look at those in the context of a career of this length, whereas it wouldn't be from season to season.

Home IP: 1158.0
Away IP: 1166.1

ERA Home: 2.48
ERA Away: 3.04

BB/9 Home: 2.9
BB/9 Away: 3.4

K/9 Home: 9.5
K/9 Away: 9.1

WHIP Home: 1.045
WHIP Away: 1.167

HR% Home: 2.2%
HR% Away: 2.1%

BABIP Home: 0.252
BABIP Away: 0.266

When I look at those numbers, the most interesting difference to me is the BB/9 rate. That's a significant gap, and one that definitely has an impact on his WHIP delta. Why was he walking more batters outside of LA? That's not a park effect. Some small disparity exists from umpire subconscious bias as I mentioned, but not that much, I wouldn't think. The differences in BABIP are probalby entirely explainable through park differences and his BB/9 & K/9 rates. I don't think there's much delta attributable to luck over that sample size, and the delta is narrow enough that it is within expectation. There is an expectation also though of a player's general discomfort level when on the road. People just perform better at home. I definitely acknowledge he was better at home than on the road, but I don't see anything that looks wildly out of line with expectations. The BB/9 rate is the most interesting part to me though. Pitching in Dodger stadium definitely helped too.