Arizona Interim GM Jerry DiPoto, via Nick Piecoro of AZCentral.com
“He’s a pedigreed major league pitcher who has accomplished quite a bit. I believe it’s a .630 winning percentage in his major league career. We’re getting a pitcher for our major league club who comes in and delivers a message to our guys that this is about winning now and winning in the future.”
Jerry DiPoto has been largely panned for this statement on why he traded Dan Haren for a package including Joe Saunders and prospects, particularly among those in the sabermetric community. Of course, we know that pitcher wins don’t tell the whole story; after all, how many times have we seen a pitcher have a win blown by his defense or the lineup, and how many times have we seen a pitcher bailed out by spectacular run support?
However, with enough games, these things tend to even themselves out, and wins begin to track true talent. Looking just at starters with at least 690 innings pitched, winning percentage and ERA+ correlate strongly, with r^2 = .500. ERA+ is a simple statistic to use here, but I feel that it works given the sample, and the park adjustments come into play as well. Obviously, correlation doesn’t imply causation, but for the most part, pitchers that receive a win in most of the games that they start are better.
This is a pretty simple conclusion to make, but it does, in part, justify the statements made by Jerry DiPoto. Joe Saunders has a 54-32 career record, good for a .628 winning percentage, good for 16th all time among pitchers with as many innings pitched – 692 – as Saunders. Some pitchers with similar winning percentages? Juan Marichal, Dwight Gooden, Roy Oswalt, Rich Harden, and Justin Verlander – a pretty solid group. If Saunders’s true talent was indeed akin to these pitchers, this trade would not be so widely panned.
Saunders, however, simply isn’t that good. The correlation between winning percentage and ERA+ isn’t perfect, and Saunders is a great example of that.
We see Saunders is well below the ERA+ that we would expect given how many of his games he has won. That’s because Saunders has spent his career playing for good teams, for the most part, and also with decent defenses. What about his counterpart in this trade, Dan Haren? Haren’s 120 ERA+ is well above what we’d expect from a player who has won 55% of his decisions, although it’s not terribly out of the ordinary – Erik Bedard, Cole Hamels, and Kevin Appier have similar careers.
One of the largest differences between winning percentage and ERA+ comes from Haren’s former Diamondbacks teammate, Brandon Webb. Webb’s 142 ERA+ is nothing short of elite, ranking fourth among players with at least 690 IP and 95% of their appearances as starts, right between Roger Clemens and Randy Johnson. However, Webb has only won 58.4% of his decisions, well below the 65.8% mark from Clemens and the 64.6% from Johnson. Why? The Diamondbacks haven’t been as good as a team as the Angels or most of Clemens and Johnson’s teams. Outside of the 2007 playoff season, Arizona has had 3 seasons with win totals in the 70s, one in the 80s, and this year’s team is on pace to win 61 games.
Simply put, in many situations, DiPoto would be right to go after the pitcher with the higher winning percentage. I’m not sure that he actually used winning percentage in his evaluation – that may just be a media talking point. Regardless, this is just another example of how we need context with all of these stats, and particularly with statistics like wins. With context, it’s clear that Saunders’ winning percentage doesn’t mean he’s an elite pitcher, and Dan Haren and Brandon Webb are good to great pitchers despite poor luck in the win column.
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