The DH has been around for almost 40 years, but baseball fans still seem to enjoy debating its merits. While some prefer the increased offense associated with the American League style, others favor the small ball strategies accentuated by the National League approach. In many ways, the give and take is baseball’s equivalent of the old “Less Filling, Taste Great” debate. What side one comes down on is merely a matter of personal preference.

Although statistics can’t answer whether having a DH is better than allowing the pitcher to hit, we can use numbers to address another popular (and related) debate: who has the advantage in interleague play?

Top-10 Pitchers in Interleague Play, Ranked by PAs

Note: Data as of June 21, 2011
Source: Baseball-reference.com

Anyone who has watched the Yankees on YES should be familiar with one side of the debate, which is frequently argued by Michael Kay. According to the broadcaster, the advantage belongs to the National League because its pitchers are more adept at handling the bat. As a result, when American League teams hit the road during interleague play, the drop off between DH and pitcher acts like a ball and chain.

Top-10 DHs in Interleague Play, Ranked by PAs

Note: Data as of June 21, 2011
Source: Baseball-reference.com

A counter to that position suggests that because National League pitchers aren’t very good at hitting anyway, the advantage they enjoy is minimal. However, when the games are played in American League ballparks, having a defined DH gives teams in the junior circuit an edge over their National League counterparts, which frequently employ a bench player in that role (even when a defensively challenged player is used as the DH, a bench player is still needed to take his place in the field).

Both sides of the debate seem to have anecdotal merit, so, what do the numbers say?

Relative Performance of DHs and Pitchers in Interleague Play

Note: Data as of June 21, 2011
Source: Baseball-reference.com

As expected, American League DHs have posted an OPS that is 0.084 points higher than their temporary NL counterparts, while NL pitchers have bested their junior circuit peers by 0.070 OPS points. At face value, the advantage seems to belong to the American League, especially because DHs bat almost twice as much as pitchers during interleague play (2.0x in the NL and 1.7x in the AL). However, because the OPS difference for pitchers is working off a lower base, the National League actually enjoys a 22% edge in that regard, compared to the American League’s 11% advantage in terms of DH production.

Because it doesn’t look as if we’ve settled the debate just yet, let’s throw in one more wrinkle: pinch hitters. Is the American League better off in an NL ballpark because it can use a quality hitter (the DH) off the bench? Or, does the National League get the edge because its reserves often get substantial playing time and have more experience serving as a pinch hitter? Once again, a case can be made for either argument.

Relative Performance of Pinch Hitters* in Interleague Play

*Based on all pinch hitters used to replace a batter hitting in the ninth slot. Pinch hitters used for pitchers batting in other slots have been omitted, and pinch hitters replacing a ninth place batter who is not the pitcher have been included.
Note: Data as of June 21, 2011
Source: Baseball-reference.com

Neither league has really had much luck with pinch hitters during interleague play. Surprisingly, even star DHs like David Ortiz (1 for 16), Frank Thomas (2 for 14), and Hideki Matsui (1 for 10) have struggled when called upon to take one at bat. At the same time, experienced NL pinch hitters like Lenny Harris (3 for 24), Mark Sweeney (1 for 24), and Matt Franco (2-15) also did poorly.  Apparently, coming off the bench isn’t such an easy task when facing the other league (having to face unfamiliar pitchers probably doesn’t help).

Aggregate Performance of DHs, PHs and Pitchers in Interleague Play

Note: Data as of June 21, 2011
Source: Baseball-reference.com

In 13,852 interleague-related plate appearances, National Leaguers have produced a line of .220/.288/.342. Meanwhile, in 14,145 such plate appearances, the American League’s output has been .218/.292/.348. Considering the voluminous sample size, the similarity in performance is astounding.

Select Statistical Totals for DHs, PHs and Pitchers in Interleague Play

Note: Data as of June 21, 2011
Source: Baseball-reference.com

Before concluding, it’s worth pointing out there are two areas in which the National League has enjoyed an advantage: sacrifice bunts and double plays (see chart above). So, with all else being equal, perhaps the senior circuit’s small ball philosophy has given it a slight relative advantage? Unfortunately for the NL, those fundamentals haven’t been enough to overcome the AL’s overall interleague superiority, which, as this analysis shows, is not derived from having an extra hitter.

Historical Interleague Record

Note: Data as of June 22, 2011
Source: MLB.com

After crunching the numbers, it’s apparent that both leagues enjoy a significant statistical advantage when playing interleague games in their home ballparks. What’s more, the respective edges seems to cancel each other out when considering all participants impacted by the different set of rules. So, as it turns out, both sides of the debate are correct. Or, maybe they’re both wrong? Here we go again.