Does the DH give the American League an advantage over the National League ?

In recent days the DH has once again been a hot topic, both Nationally and here in the comments sections at the AZSnakepit. One specific aspect of the discussions prompted me to take a closer look at just how much of an advantage the DH gives the AL over the NL. It certainly affects roster construction, as AL teams are more likely to have defensively challenged sluggers on their roster while the NL game requires more defensively oriented and position flexible utility players coming off the bench. So it’s fairly obvious that the AL DH’s are likely to be stronger hitters. However intuitively, it would seem that NL pitchers are better hitters than AL pitchers, so that might offset the AL “roster construction” advantage. We’ve discussed this in the past, but I felt it was time to do a bit deeper dive on the matter, and see where the data takes us.

First, as always, CONTEXT. There can be little doubt that the AL has dominated interleague play for a long time. In fact the AL had an unbroken streak of 14 consecutive years with a winning record vs. the NL going back to 2003. That streak was broken in 2018 as the NL finally posted a winning record. Wikipedia has a pretty good summary of the seasonal records HERE

The NL actually had the better record in 4 of the first 7 seasons of interleague play before that 14 year drought. Here is a quick summary of all time, and also the last 10 years, which is the data set I’ll be using below.

So that is fairly definitive. The AL has had a sizable advantage in head to head play. Websites such as Fangraphs and Baseball-Reference also calculate relative league strength, or League Equivalencies . They do this by comparing how players who played in different levels, or different leagues in the same year or year over year performed. Regression models are used on that data, and it gets pretty complicated. However on a per player basis, this is usually worth up to 1-2 runs difference in the value/WAR calculations. It may not seem like much, but these add up on a team basis. Over the last 10 years, AL teams on average are credited with roughly 10 runs extra per year in WAR calculations, or approximately 1 WAR . This works out to about a .012-.013 difference in Win % . Thats actually less than half the actual WL % difference we have seen in head to head play. So while some may take objection to these sites crediting the AL for being the tougher league, if anything they might be understating it.

SO....the AL is stronger than the NL. This is fairly well established. The question then becomes, how much of this can or should we attribute to the supposed “unfair advantage” the AL has due to the DH, and the impacts it has on roster construction. Full disclosure, I have thought or believed this was a significant factor, and have stated so on the pages of this website in the past. SPOILER ALERT: I may have been wrong, or at the least, vastly overstated the effect. Lets take a look.

All the stats I’m using below are the last 10 years of interleague split data from Fangraphs. I felt that is a large enough sample to work with, while at the same time keeping things more current.

DH COMPARISON

Well, this should come as no big shock. AL DH are significantly better than NL DH in head to head games. Some of this is definitely the road park penalty, as most hitters hit better at home than on the road, (MLB OPS H/R Split in 2018 was 20 points in favor of the home team). By definition, at least for the next year or two, all NL DH are on the road. But 73 points of OPS, 30 points of wOBA and 21 points of wRC+, as well as a raw total 127 runs created show pretty clearly that this part of the equation tilts decidedly towards the AL.

PITCHERS BATTING COMPARISON

Here we also see as expected the NL pitchers are hitting a lot better than AL pitchers. Again, some of that his the home park advantage, but most of it is probably as we’d suspect, lack of reps for the AL pitchers. SO a sizable chunk of the AL advantage is indeed eaten away here. The pitchers PA’s are a lot less than the DH PA’s, so some of that NL advantage is muted due to fewer PA’s.

But wait, what about pinch hitters ? Another piece of this puzzle that needs to be taken into account is pinch hitters. After all, how many times have heard the announcers remind us that the visiting team’s big bopper DH is waiting in the wings to come in and pinch hit at a critical moment in games in NL parks. Surely David Ortiz or Nelson Cruz lurking on the bench presents more of a threat than a Chris Owings or Daniel Descalso

PINCH HITTERS

Turns out, on a macro basis, not so much. It’s basically a push. Thats kinda surprising perhaps, but as I think about it, not only do NL Pinch Hitters usually have the home field advantage, (presuming most AL PH at bats are for the pitcher), but NL PH are also more used to preparing for just one PA. Pinch hitting is hard to begin with. .212/.300/.339 .639 OPS last year. So perhaps these results should not feel so shocking.

Lets total it all up. DH, Pitchers, and Pinch hitters:

These overall results were surprising to me. I assumed that the DH and PH advantage for the AL far outweighed the pitchers hitting advantage for the AL. But it simply hasn’t been true over the past 10 years. The advantage is in fact very small, and certainly does not come near explaining the success the AL has had over the NL in interleague play. This is a classic case where I was guilty of confusing what I believed with what I actually knew. Happens to the best of us ;)

So if the advantage is not due to the DH, or as has just been shown, the advantage for NL pitchers offsets most of the AL DH advantage, why has the AL won so many more games ? Well, looking at all the rest of the hitters, i.e. NON DH, Pitchers and PH the gap starts to look pretty large.

One last table though, a quickie pitcher view

The interesting thing here is how much larger the era gap is between relief pitching compared to starting pitching, almost half a run. How much of the AL advantage is due to better pitching, or fielding, or hitting is not something I have figured out how to tease from the numbers yet. But most likely it’s simply a combination of better players overall leading to the AL dominance over the years. WHY do they have better players ,? Is it simply higher payrolls, or better drafting and player development and overall management ? I don’t know.

What we do have a clearer picture of though is the AL advantage is not really due to the DH.

I stand corrected.