The Perfect Speed for a Fastball: 97 MPH

During the 2006 postseason, baseball introduced a new system for analyzing pitches that is accelerating the transition of pitching from art to science.

Pitch-f/x is a system of sensor cameras that track the movement and velocity of pitches to within 1/2-inch of their actual paths. This season marks the first time that all major league ballparks are equiped with Pitch-f/x technology. The possibilities for statistical research with this data (which you can download yourself) are mind-boggling.

The most fantastic example of this is blogger Dave Cameron, who posted an open letter to Seattle Mariners pitching coach Rafael Chaves arguing that staff ace Felix Hernandez was throwing too many fastballs to start games, and getting himself into trouble in the process. Amazingly, Chaves came across the letter, printed it out and gave it to Hernandez. In the next game, the pitcher threw eight shutout innings and gave up only two hits. After the game, Hernandez said:

"Chaves gave me a report...on the internet, they say when I throw a lot of fastballs in the first inning, they score a lot of runs. I tried to mix all my pitches in the first inning.''

Now, over at Statistically Speaking, Eric J. Seidman has dissected baseball's most famous pitch: the heater. Using Pitch f/x, Seidman went through and collected data on 130,000 fastballs and some of the results are fascinating.

But first, here's an unsurprising result: faster fastballs are correlated with more strikes:

But these next two charts show that there are diminishing returns to speed:

Most surprising, the batting average on balls in play for pitches thrown at 97 MPH drops by about 20 points! Seidman doesn't think this is a result of a small sample size, so what's going on? The combination of speed and movement appear to arrive at a sweet spot of sorts at around 97 MPH:

Something interesting to consider was how, in each of these tables, all patterns seemed to stop when they reached 97 mph or higher. The horizontal movement increased instead of its decreasing trend; vertical movement decreased after its increase at 97; the percentage of strikes ceased increasing; and home runs reached their low. Could be something, could be nothing, but interesting nonetheless.

I also wonder if there is something geometric going on here. Maybe at 98 MPH and above there isn't enough distance for a fastball to work its magic on a batter.

(Hat tip: Taylor Umlauf)

UPDATE
Upon further reflection:

In the 97 mph group, the four pitchers with at least 5% of the sample combine to represent 23% of the total. For 98+ mph, the eight pitchers with at least 5% of the sample combine to represent 56% of the total.
From these results it seems that 92-96 mph are safe from a drastic case of small sample size syndrome. Anything abobe 97 mph, though, seems to be the opposite as they suffer from a small sample of balls in play as well as skewed results due to a small group of pitchers representing most of the total pitches.

In other words, the sample size itself could be large enough, but the number of pitchers who throw 97 MPH and above are smaller than in other groups, hence introducing a bias into the results. -We'll have to wait for more pitchers throwing more heaters to clear things up.

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