Heater Getting Hotter

Yesterday we looked at the averages of fastballs from different velocity groups as a means to compare certain pitchers to their like-throwing peers as opposed to an extremely broad group.  This way, we can compare Matt Cain’s movement to the average movement for all 94 mph fastballs to determine how effective it has been.
In doing so an anomaly surfaced: all velocity groups had a BABIP between .290-.310 except those thrown 97 mph.  Those heaters registered a .273 BABIP, nearly 20 points below the others.  Sure enough, fastballs registering 98 mph or higher jumped back to .293, leading many of us to believe something screwy, flukey, or any other adjective ending with the suffix “-y” slapped on its end, was taking place.  After exploring some logical possibilities, like a split-half reliability test, or a look at BABIP by count and location, the results either stuck or were inconclusive due to small sample sizes at work.
We had a really nice discussion in the comments section wherein more possibilities were tossed around.  The first of these suggestions involved testing the sample size via a Bernoulli Trial.  As was shown by commenter Adam Guetz, for an observed .273 when a .295 was expected, we would need approximately 1,650 balls in play.  For 97 mph pitches there were 707 balls in play, less than half of what is required, and just 325 balls in play for 98+ mph.  While the sample sizes of actual pitches thrown are large enough to conduct certain analyses, those of balls in play for anything 97 mph or higher were not.  Here are the BIP sample sizes:

  • 92 mph, 18.85 % BIP and 7,759 total
  • 93 mph, 18.05% BIP and 6,023 total
  • 94 mph, 18.05% BIP and 4,389 total
  • 95 mph, 17.04% BIP and 2,827 total
  • 96 mph, 17.26% BIP and 1,596 total
  • 97 mph, 16.69% BIP and 707 total
  • >98 mph, 16.11% BIP and 325 total

The samples from 92-96 appear large enough, but the combination of 97 and 98+ still comes a good 500 pitches below 96 mph on its own.  Another suggestion called for the total number of different pitchers as each interval as well as the number of those comprising certain percentages of the samples.  This way, we might be able to deduce that 97 mph pitches were skewed due to a small group representing the whole; for the lower velocities, which are more common, it is much more likely for the pitches to be more evenly divided amongst a larger group of pitchers.  Here are the number of pitchers for each group, those comprising 1% of the sample, and those comprising 5% of the sample:

  • 92 mph: 574 total pitchers, 8 at 1%, 0 at 5%
  • 93 mph: 485 total pitchers, 18 at 1%, 0 at 5%
  • 94 mph: 516 total pitchers, 21 at 1%, 0 at 5%
  • 95 mph: 337 total pitchers, 25 at 1%, 0 at 5%
  • 96 mph: 237 total pitchers, 28 at 1%, 1 at 5%
  • 97 mph: 160 total pitchers, 25 at 1%, 4 at 5%
  • >98 mph: 102 total pitchers, 18 at 1%, 8 at 5%

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. 
Another commenter, Dave Evans, pointed out that he received a significance of 0.55 when comparing 97 and 98+, meaning their BABIPs were not statistically significantly different; for significance, that value would need to be equal to or below 0.01.  This led me to group 97 and 98+ together, to enlarge the sample.  The result was 1,032 balls in play, 288 hits in play, and a .279 BABIP.  This suggested the possibility that perhaps it was not 97 mph that deserved the adjective+suffix “-y” treatment but rather 98+ mph pitches.  Granted, it is still a small sample, even moreso for BABIP, but perhaps we will find out, as more data becomes available, that 97 mph is the threshold, as Pizza Cutter noted, for “blowing it by the hitter.”
It will require several hundred more pitches in play to determine this with any certainty but I will be keeping very close tabs as the season progresses.  For now, though, we can effectively compare individual pitchers to the average movement components, B%, K%, and BABIP for their specific velocity, not an entire group, at least for heaters 92 mph to 96 mph.

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