Debunking more fastballs in the American League

For the last several years, it’s been thought that the American League is a breaking pitch league — that is, the caliber of hitters in the AL dictate that fastballs should be relied on less. If you are a fastball hitter, you want to go to the National League where you can dominate. On the face of it, this seems not to make sense based on the fact that junkballers are the ones that benefit most from a move to the NL.

In any event, this disparity between the leagues is a commonly accepted belief.

The problem? It’s just not true.

In research for my various articles to write, this question of fastball effectiveness per league came up. I did not want to state the anecdotal belief without some hard evidence, so I turned to Lee Perrault from Fire Brand (a Red Sox blog I write at) who is great with Pitch F/X.

He found no such fastball disparity between the leagues.

Over the last three years, 58.09 percent of all pitches in the National League were fastballs, amounting to 465,727 of them.

In the American League, their 428,558 fastballs ranked 59.06 percent.

Not only is incorrect that the National League is the fastball league, but the American League actually holds the edge in seeing fastballs. This is particularly significant because without the designated hitter in the NL, you would think a higher volume of fastballs would be thrown to pitchers. If we assume just that, then the fastball reliance on hitters 1-8 (or 1-7 and 9 on Tony LaRussa’s team) only decreases. A junkballer’s haven, indeed.

My next step was to see if perhaps this commonly held belief was based on production off the fastball, not volume. In other words, maybe the AL really is more effective against fastballs despite it being thrown more.

The AL OPS against fastballs was .745. In the NL, it was .727. Is that significant enough?

Pitchers OPS’ed at .353 over the 2007-9 span (the years the fastball data covers) in 17,771 plate appearances across both the AL and NL. NL plate appearances amounted to 300,349 over this time span, while NL pitchers were responsible for 16,800 of the plate appearances. This means that pitchers were responsible for roughly 1/18th of the plate appearances in the National League. Even if you assume a slight tick up in OPS (to account for American League pitchers being part of my sample), the math comes out to the NL OPS of non-pitchers against fastballs being roughly the same as the American League (h/t Daniel Moroz at Camden Crazies for the concept, Eric Seidman of Baseball Prospectus for the data).

My conclusion?

The anecdote of the American League being more of a breaking-pitch league is incorrect: it’s the National League. That also confirms the other anecdote about junkballers benefiting from a move to the NL. However, this anecdote is strictly based on the fact that there is one less position player to pitch to: both leagues produce at the same level against fastballs.

Here is the full offensive breakdown of league production against fastballs*:

* One thing I didn’t tackle but noticed is the difference between the league’s OBP being rather small compared to the difference in slugging percentage.

American League
# of fastballs 428558
singles of fastballs 61557
doubles of fastballs 18592
triples of fastballs 1824
HRs of fastballs 10277
walks of fastballs 55166
HBP of fastballs 3129
INT BB 284

OBP 0.351945361
SLG 0.392781752
OPS (AL) = 0.744727113

National League
# of fastballs 465727
singles of fastballs 64258
doubles of fastballs 19671
triples of fastballs 2395
HRs of fastballs 10583
walks of fastballs 60033
HBP of fastballs 3459
INT BB 459

OBP 0.345391184
SLG 0.381100414
OPS (NL) = 0.726491598

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Cisco Bastidas
14 years ago

For me just coming to this site, looks like mathematician haven….good inside info…keep it up!…