Tonight begins interleague play, and the American League seeks to extend their recent run of domination. They’ve taken the season series six times in a row, and the margin hasn’t been less than 20 games since 2004. While there’s some reason to think this year might be might be closer – the NL has actually been outscoring the AL so far – is the basic concept of interleague play biased towards the AL?
Does Interleague Play Favor the American League?
The theory goes like this: AL teams are used to the DH, and he is usually the best or nearly the best hitter on the team. NL outfits, however, are used to playing with eight batters, and when they need to find a DH, that tends to mean the ninth-best hitter on the roster gets into the line-up. But do the statistics back this up?
It doesn’t appear necessarily to be the case. Last year, NL batters in the DH role during interleague play had a line of .277/.357/.457. The resulting OPS of .815, was actually 35 points higher than American League DH’s posted over the whole season (.255/.337/.443). However, in 2008, the difference was as the theory predicts, 59 points of OPS in favor of the AL, .775 to .716.
But countering this, is AL pitchers having to bat. Tonight’s game between Toronto and Arizona illustrates this nicely. Diamondbacks pitcher Dan Haren is 10-for-25; Blue Jays pitcher Brandon Morrow has three plate-appearances. That’s not three plate-appearances this season. Or even three major-league plate appearances. That’s three plate-appearances in his entire professional baseball career, including the minors.
That’s a benefit that extends across the entire league. In 2009, NL pitchers had a collective OPS almost a hundred points better than their AL brethren (.355/.257). In 2008, it was less, but still present (.354/.312). It seems likely that this edge goes a significant way to defusing any benefit conferred by a roster built around the DH.
(Ed. Note: On the first night of Interleague Play, the American League won eight games to the NL’s six.)
See More:
