What Is Baseball's More Powerful League, the AL or NL?

Zachary D. Rymer@zachrymerMLB Lead WriterMay 16, 2013

Which of Major League Baseball's two leagues features more muscle? The American League or the National League?

I don't have the time, the energy or the clipboard, but if I were to go around and survey baseball fans, I'm guessing the general assumption would be that most of the power resides in the American League. It's the league that has the designated hitter, after all, and American League lineups are deeper than National League lineups by reputation.

It's true that the American League does feature more power than the National League, but you might be surprised to hear that that it wasn't as clear-cut for a while there. For about a decade, the Senior Circuit had the power to rival the Junior Circuit.

How do I know this? Meh, just a hunch. You can trust me.

...Actually, it's because I looked at the numbers and saw some things.

My investigation had a simple beginning. All I was interested in at first was how much better or worse the American League has been at racking up extra-base hits since the inception of the DH in 1973. To this end, I went over to FanGraphs and dug up some league ISO data.

If you're not familiar with ISO, it stands for Isolated Power, and the best way to think of it is as a slugging percentage that ignores singles. It's only concerned with doubles, triples and homers and can be calculated simply by subtracting a batting average from a slugging percentage.

This graph shows the progression of the American League ISO by year since 1973 as compared to the National League ISO since then:

You can see that the American League had the edge in power for many years, but that the gap closed in 2000 and then there was some jockeying for position. Up until the last couple years, the National League was holding its own against the American League in the power department.

Huh? What's that? An elephant in the room?

Oh, right. Pitchers.

With the exception of Yovani Gallardo, pitchers can't hit much, and you're right to assume that they're skewing the data for the National League. Luckily, FanGraphs makes it easy to remove them from the equation for the AL and the NL to make a graph that looks like this:

Here, you see less of a defined edge for the American League from 1973 to the turn of the century, and that, for a while there, the National League was the superior power-hitting league.

If we break it down by time periods:

Span AL Avg. Non-P ISO NL Avg. Non-P ISO
 1973-1979  .123  .124
 1980-1989  .136  .126
 1990-1999  .150  .146
 2000-2009  .160  .164
 2010-2013  .153  .150

Since the DH was spawned in 1973, the American League generally has been the better power-hitting league. But the National League was the better power-hitting league by a small margin in the 1970s and by a wider margin from 2000 to 2009.

That had much to do with the big step forward the National League took with its home run production. Drawing American League data and National League data from Baseball-Reference.com, here's a look at the average home runs per game for each league in our key time spans.

Span AL Avg. HR/G NL Avg. HR/G
 1973-1979  0.77  0.70
 1980-1989  0.89  0.71
 1990-1999  1.01
 2000-2009  1.10  1.06
 2010-2013  1.04  0.93

Note: The initial version of this article included a table showing total home runs hit in these time spans, but B/R commenter Cedar Park bopped me on the head and reminded that the National League had two more teams than the American League from 1998 right up until last year. A bad oversight on my part, hence the above alteration. The rest of the article was changed accordingly.

You can see why the American League was so easily able to garner a reputation as the more powerful league, as it came to have a gigantic edge in home run production for more than a couple of decades following the installation of the DH in 1973.

But the National League caught up in home run production in a big way from 2000 to 2009, and that the gap managed to get so small is all the more impressive once you consider that pitchers are included in the equation here. Even with pitchers contributing very little to the league's home run production, the National League was nearly on par with the American League and its DHs.

It's also worth noting that there were some top-notch sluggers in the National League in this span. Between 2000 and 2009, seven of the 10 major league home run leaders came from the National League (there was a tie between Jim Thome and Alex Rodriguez in 2003).

But you can see that the American League has regained a big edge in home run production these last couple of years, just as it has regained its edge in non-pitcher Isolated Power. The Junior Circuit has also regained control of the home run leaderboard, as the last three major league home run leaders have been American Leaguers: Jose Bautista in 2010 and 2011 and Miguel Cabrera last year.

For the record, it doesn't look like anything will be changing this year. Entering Thursday's action, the AL's non-pitcher ISO was .159 and the NL's non-pitcher ISO was .150. The American League was averaging 1.10 homers per game, and the National League was averaging 0.96 homers per game.

So it was close for a while there. Real close. But the last couple of years have seen the American League regain total control of the power struggle (sorry, couldn't resist). 

Will it last?

I doubt it. The one thing that can't fairly be removed from the American League side of the equation also happens to be the very thing that's bound to find its way over to the National League side of the equation before long: the DH.

As ESPN's Jayson Stark wrote/predicted in early April, it's just a matter of time before MLB puts the designated hitter in the National League. With interleague play now an everyday thing, it's only fair that the two leagues should have rosters constructed to play the same game. That means either making pitchers in the Junior Circuit hit or putting the DH in the Senior Circuit.

Which would be better for baseball? That's a matter of opinion. What isn't a matter of opinion is that there's a business interest in this discussion, and it leans toward the DH. As Stark wrote, the DH can help prolong the careers of aging, high-paid sluggers and bar high-paid pitchers from hitting and running the bases, two things that can hurt them.

Once the DH is in the National League and the two leagues are essentially carbon copies, it's unlikely that there will be any sort of pattern to where the power lies. It's going to go back and forth between the two leagues like never before.

If so, I suppose we'll have to have a "Where's the power?" discussion every year.

To which I can only say this: I'm down.

If you want to talk baseball, hit me up on Twitter. 

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