Yesterday we showed that, over time, Wins is a good indicator of how good a pitcher is. However, with any good statistic, there are exceptions that prove the rule. Today, we will look at those pitchers for whom Wins does not indicate how well or how poorly they have pitched.
In yesterday’s post we showed that there is a strong correlation between a pitcher’s ERA+ and how often they are credited with a win. In fact, that chart gives us a formula that can be used to predict how often a pitcher will win a game based on their ERA+:
Predicted Win Percentage* = (0.0034*ERA+) + 0.0293
*In this case we are measuring Win Percentage as wins per game started. This differs from the traditional method of measuring Win Percentage in which Wins are only compared to Losses.
Using that formula, we can look at every pitcher with 600 innings pitched over the last four seasons (150ip/season) and use their Predicted Win Percentage to calculate how many games they should have won.
Surprisingly, 38 of the 51 pitchers (74.5%) were within 5 wins of their predicted total for the past 4 seasons combined (complete list after the jump). Only 7 pitchers (13.7%) deviated from their expected win total by more than 8 wins (>2 wins per season).
Not surprisingly, Josh Beckett has benefited greatly from pitching for the Red Sox the past four years. Meanwhile, Matt Cain has fallen victim to the anemic offense of the Giants. Vicente Padilla has been helped by the Rangers strong offense, having twice won 14 games despite not having an ERA under 4.50 the last 4 seasons. Meanwhile, Jarrod Washburn and Zach Duke have lost a lot of games despite pitching close to league average.
On the other hand, we were surprised to see how lucky Justin Verlander has been with the Tigers, especially when one considers that he went 11-17 last year.
Still, the most surprising aspect of all of this is that only 7 of the 51 pitchers deviated by more than 2 wins per season over the last 4 years. That is the same number of pitchers that were within 1.5 wins of their expected win total, further supporting the notion that Wins is indeed a good evaluator of a starting pitcher.
Full list of pitchers expected wins versus observed wins after the jump…