Truth Lies in the Numbers
Pitchers’ ERAs Almost Always Rise and Fall With Switch From One League to the Other
When a starting pitcher switches leagues, it is generally assumed he will see an adjustment of around three-quarters of a run to his ERA, resulting from the fundamental differences between the American and National leagues. Sometimes the change is far more dramatic.
So, it is perhaps not surprising that Ramon Ortiz has gone from a 5.57 ERA last year in Washington to a 1.80 ERA through his first two starts this season for Minnesota.
Or that Steve Trachsel (4.97 ERA with the New York Mets last year) has a 2.63 ERA for the Baltimore Orioles through two starts.
Or that Barry Zito, the most expensive free agent pitcher in history, has gone from a 3.83 in Oakland last year to an 8.18 through two starts in San Francisco.
But hold on a minute. Those examples are all backward. Ortiz and Trachsel, moving from the NL to the AL, are supposed to see their ERAs rise — owing largely to the presence of the designated hitter in the junior circuit — while Zito, going the opposite direction (and to an extreme pitcher’s park at that), should be seeing a drop in his ERA. What’s the deal? “You may assume my ERA is going up because I switched leagues,” Trachsel said. “But I don’t.”
With all due respect, Mr. Trachsel, we chalk up these statistical anomalies to the small sample sizes from 2007. When all is said and done, we expect Trachsel, Ortiz, Zito and all the other league-switchers to fall in line with recent history, which says it is virtually a given that a pitcher going from the NL to the AL will see a rise in ERA, while a pitcher moving in the opposite direction will see a drop.
“The DH, obviously, is a huge dynamic,” said Detroit Tigers closer Todd Jones, who has switched leagues five times. “But it’s more than that. There are differing theories of team-building. In [the AL], with a middle infielder, they’ll still take a bat over a glove. In the NL, they’ll take a glove. It’s not that it’s easier in the NL, it’s just different. In the NL, they’ll bunt and play small ball. But here, it’s a lock-and-load league.”
Orioles pitching coach Leo Mazzone, himself a league-switcher in 2006, takes it a step further: “Look at the No. 9 hitter,” he said. “In the NL, it’s a pitcher. In the AL, not only is it not a pitcher, but it’s usually a burner — he’s like a second leadoff hitter. So it’s like you’re facing back-to-back leadoff hitters.”
The last class of league-switchers for which there is a full season’s worth of data proves the point. In 2006, 10 pitchers who had thrown at least 100 innings in the NL in 2005 switched to the AL. Eight pitchers, meantime, made the opposite switch. Of those 18 pitchers, all but one experienced the expected rise/drop in ERA — an average rise of .78 for those who moved from the NL to the AL, and an average drop of .85 for those who went the opposite way.
The only pitcher who bucked the trend, Vicente Padilla (who went from 4.71 in Philadelphia to 4.50 in Texas), had the benefit of leaving one of the most extreme hitters’ parks in the NL.
When you expand the list to include other prominent pitchers who switched leagues in recent years, they almost uniformly followed the pattern. (Interestingly, the most prominent trend-bucker, Kevin Millwood, was another who, like Padilla, made the smart career move of fleeing Philly’s launching pad.)
So rejoice, Randy Johnson and Mark Redman — you lowered your ERA before you threw your first pitch this year. And pray, Jeff Weaver and Tomo Ohka — hope you like higher ERAs.
As for you, Roger Clemens (and we know you pay attention to these things), keep this trend in mind as you decide whether you really want to go back to the AL this year.