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Talking Sabermetrics: Pitching in the American League

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We look at pitching data regarding AL/NL differences as the Astros prepare for the great move.

Doug Pensinger - Getty Images

A recent theme for the "talking sabermetrics" series is the Astros' move to the American League. Perhaps you were trying to suppress thinking about the Astros' move, pushing it to the deep recesses of your mind. But it's true. The move will happen. And sooner rather than later.

For today's article, we will look at some statistical nuggets about the difference between AL and NL pitchers.

Do NL Pitchers Throw More Fastballs?

This is something I've heard for 30 years. Supposedly National League pitchers use the fastball more frequently than American League pitchers. I assumed it was true. But the data doesn't support this claim. If anything, in recent years AL pitchers relied more heavily on the fastball than NL pitchers.

Because base stealing traditionally is viewed as a more important tactic in the NL, people surmise that NL pitchers will throw more fastballs in order to control the running game. Perhaps the adage about NL pitchers throwing more fastballs was true at one time. But over the years, many coaches and pitchers have changed leagues. I wouldn't be surprised to see differences between the leagues decline over time.

This 2009 Hardball Times article used pitch f/x data over a three year period to debunk what it called the "myth" of higher fastball usage in NL. 58.09% of total NL pitches were fastballs, compared to 59.05% in the AL. The article also points out that the adage about NL reliance upon fastballs contradicts another adage: junk ballers improve their performance moving from the AL to the NL.

Does the conclusion from the 2009 article still hold up?

I examined fangraphs data on AL and NL teams' pitching usage. By using data at the team level, the data will reflect the actual usage of pitchers, so that there is no need to separate relievers and starters. In both 2011 and 2012, the median team fastball percentage is higher in the AL than the NL.

The average fastball percentage for a AL team is 58.06% compared to 57.16% in the NL.

Some would suggest that pitchers batting in the NL would see more fastballs than the average hitter, since they are less experienced hitters. And, if that is true, it suggests that the AL advantage in fastball usage must be even higher for pitches seen by non-pitchers.

Another bit of speculation you sometimes hear is that AL pitchers throw more breaking pitches because the sluggers are so good that they have to resort to "fooling" them. However, the data on AL fastball usage doesn't support that notion. We often hear hitters say that the best pitch is a well located fastball. And that may explain the AL fastball percentage.

Other Pitch Types and Velocity

Not only do the AL teams throw a higher percentage of fastballs, but the average velocity is higher than in the NL. In 2012, the average AL team's FB velocity is 91.88 mph, compared to 91.28 mph in the NL. Since fastball velocity generally is correlated with pitching success, this may suggest that AL pitching is better than NL pitching. However, this observation is far from proving that as a fact.

Now let's look at other types of pitches and see if the percentage usage favors either league. The data reflect the average 2012 AL and NL team, with italics used to show the league with highest usage for a pitch.



Slider 13.93 / 14.81

Cutter 6.19 / 5.4

Curveball 10.0 / 10.6

Change Up 10.18 / 9.56

Admittedly the differentials generally are small, so don't read too much into the league differences. The data shows that the NL tends to throw the slider and curveball more, while the AL pitchers are more likely to throw cutters and change ups. The change up in the AL is 1.27 mph faster than in the NL, which is consistent with an average fastball that is 0.6 mph faster. Maybe AL pitching strategy relies more on "fooling" hitters---if you consider the change up as the pitch most aimed at tricking batters.

Junk ballers

As noted previously, there is a general assumption that junk ballers and soft tossers can fare better if they move from the AL to the NL. I don't have a definitive answer to that question. But the 2012 data, above, suggests that the average velocity for NL pitching is lower, and perhaps relies more on traditional breaking pitches than the AL.

Looking at the Fangraphs 2012 leaderboard for qualified pitchers, the NL has twice as many pitchers (10 to 5) with an average FB velocity below 89.5 mph. The AL has no qualified pitchers with a FB velocity below 86 mph, while the NL has three. There were two more teams in the NL, which may explain some of the difference. And we are looking at small sub-groups, which limits our conclusions. But the comparison doesn't dispel the notion that soft tossers may have a safer haven in the NL.

This makes me wonder if a soft tosser like Keuchel will have a tougher time moving to the AL. Keuchel had the lowest average velocity (89.0) among Astros' starting pitchers, followed by Edgar Gonzalez (89.5).

In addition, the Astros' bullpen seemed to lack high velocity arms, even by NL standards. Without some reinforcements, the Astros' bullpen may appear even worse when it faces AL hitters.

Rhiner Cruz (95.0) had the only bullpen arm comparable to the higher end velocities frequently seen in other teams' bullpens. However, Cruz's control and command issues limited his usage in high leverage situations.

Setting aside Cruz, Fernando Rodriguez (93.9) was the power arm in the bullpen, and his velocity isn't elite. Jose Valdez (93.8) had the next highest average velocity out of the bullpen, but I would not put too high expectations on a career minor leaguer.

Use of Pitchers

The DH has some direct impacts on the way pitchers are used in AL. NL pitchers may be removed from a game for non-performance reasons; in other words, the offensive situation may compel the need for a pinch hitter. AL pitchers are more likely to be removed for bad or deteriorating performance.

As pointed out by this 2009 analysis (for fantasy purposes) at the Hardball Times, the AL starters tend to throw deeper in games and are more likely than NL starters to be removed in the middle of an inning. Not surprisingly NL starters are more likely to be removed at the end of an inning than AL starters.

Comparing 2012 data at Baseball-Reference, AL teams average 5 complete games, while the average NL team has 4 complete games. (The Astros had 3 complete games, in case you were wondering.) The average AL starter threw 1 more pitch per game started than the average NL starter in 2012. The countervailing effect of the DH on starting pitcher usage is that the AL lineups are tougher, making starting pitchers more susceptible to removal for performance reasons. That may explain why AL pitchers pitched the same number of innings per start as NL pitchers in 2012. The AL pitcher's tendency to pitch deeper due to the DH appears to be offset by more pressure for performance related pitcher removals.

The DH indirectly affects pitcher usage patterns based on its impact on the roster. With a DH, teams may have less need for pinch hitters, allowing teams to carry more bullpen pitchers. Since starting pitchers are more likely to be removed mid-inning than in the NL, the use of bullpen platoon specialists becomes more frequent. As Cee Angie noted in her TCB article, this creates a need for more hitting specialists, resulting in a roster dilemma for AL teams.

According to Baseball-Reference data for 2012, lefthand batters and lefthand pitchers in the AL constituted larger percentages of total plate appearances than in the NL (46% to 42% among batters and 30% to 29% among pitchers). This is consistent with greater use of platoon specialists for both batting and pitching in the AL. But in the AL, pinch hitters are used in situations with 16% more leverage than pinch hitters in the NL. (This isn't surprising, given the effect of the DH.)

Some thoughts: don't expect the need for fewer LOOGYs or less platooning of batters when the Astros move to the AL. If anything, there will be more pressure for platooning on both offense and defense.

How will this affect the Astros' roster decisions?