In 1973, the owners of the American League adopted Major League Baseball rule 6.10, which allows any league the option to use the Designated Hitter rule. Ever since, fans of each league have argued the superiority of said league’s rules. National League fans prefer the more strategic, small ball style that stems from the pitcher batting, and AL fans prefer the offense that results from batting nine major league caliber hitters instead of eight.
One question that arises with this difference in rules is how much spread in batting production we see between the two leagues. The natural assumption is that pitcher hitting is relatively even between teams, as most pitchers are generally equally poor at hitting. With DHs, we would assume that we can see the wide variation that we see with all other positions.
Is this true, though? Let’s look at some data. PBWRAA is “pitcher batting weighted runs above average,” given that the average pitcher wOBA in 2009 was .164.
First, with NL pitchers, we see a roughly 20 run difference between the Pirates and the Cubs. This is a significant difference on a team level. Having Carlos Zambrano (.305 wOBA) and Sean Marshall (.242 wOBA) over players like Charlie Morton (.115 wOBA) and Ross Ohlendorf (.071 wOBA) can be a two win swing just with the bat. This is what makes Zambrano so much more valuable in the NL – his 3.95 career FIP isn’t ace quality, but with a .305 in 65 PAs as a pitcher, he contributed eight runs with the bat, nearly a win worth of production.
Similarly, Milwaukee Brewers fans likely will not soon forget how terrible Ben Sheets handled the bat during his tenure with the club. With his .096 wOBA, over that same 65 PA sample with Zambrano, he would have accrued four runs below average, for a difference of nearly 1.2 wins. That essentially offsets the roughly 10 run difference between 180 innings of Sheets (3.56 FIP) and Zambrano (3.95).
Now, let’s take a look at the spread in DH hitting.
Here we see a spread of 45 runs. However, the spread in wOBA is only 80 points vs. 63 points for the pitchers. This is because the DHs see nearly twice as many plate appearances as the pitchers over the course of the season. Taking this into account, the spread between leagues is much lower. We shouldn’t expect the inclusion or exclusion of the DH to result in any more or less parity. In other words, the difference between Hideki Matsui and Jose Guillen is similar to the difference between Cubs pitchers and Pirates pitchers at the plate. It’s also worth noting that only one team this year was below average in their league-specific category and made the playoffs – the Red Sox at -2.23 DHwRAA.
Draw your own conclusions from this data. This is not meant to endorse either rule system as better than the other, but instead to provide a comparison of the two rule systems.