Weak Contact: Mixing Speeds & Horizontal Movement

I’ve been trying to get to the root cause of how much can a pitcher limit hard contact. I’ve had some hits and misses, but today I’ll finish going over the possible inputs.

I’ve already investigated the groundball/flyball issue and generate weak contact when hitters make contact with pitches out of the strike zone in this series and previously looked into two-strike counts and found nothing. Here are the five possible causes.

  • After contact, the ball coming off the top (popup) or bottom (groundball) of the bat.
  • The batter chases a pitch out of the strike zone and makes a less than full-effort swing.
  • The batter is taken off guard by the pitch’s speed (fast or slow) and can’t make a full-effort swing.
  • The batter is deceived by the pitch’s horizontal movement and makes contact off the end or handle of the bat (h/t to Kenny Butrym).
  • With two strikes, the batter shortens up his swing just hoping to put the ball into play.

So it’s time to finish the list to see if changing speeds and horizontal movement help limit hard contact.

Pitch speed differences

Simply, I could find no correlation between changing pitch speed and generating weak contact. I measured the difference in pitch speed two ways. I took the standard deviation of all a pitcher’s pitches and compared it to various hard-hit metrics. For the other study, I found the average difference between the pitcher’s average velocity and each pitch.

Looking at all pitchers from 2020 and 2021 (Hawkeye pitch-tracking era), none of the batted ball metrics (BABIP, HR/FB, HR/BIP, ERA-xFIP, and vsISO) had an r-square over 0.004.

I limited the data sample to pitchers who threw the most pitches and BABIP’s r-squared pushed up to 0.02 for both pitch speed difference methods. I wonder if there is just some survivor bias going on because those pitchers with the lowest BABIPs were allowed to throw the most innings.

Like with the two-strike approach study that also found nothing, the inconclusive results don’t mean it’s not a factor, it’s just one I can’t measure.

Horizontal movement moving contact off the sweet spot

The more I waited on studying this idea, the more I thought I’d find nothing. The deal is that for this idea to work, the bat needs to be perfectly level at the point of contact. If the bat is even at the slightest angle, the new contact will be at the top or bottom of the barrel causing a groundball or popup depending on the hitter’s handedness and bat angle. Both results have been shown to lead to weaker contact, so going in I knew there could be some overlap.

Determining horizontal movement is not easy. I decided to go with the average difference when comparing a pitch’s horizontal movement to the league average horizontal movement. Using the same dataset as the first study, I was surprised to find some correlation.

R-Squared for Horizontal Movement to Other Factors
Stat Horizontal Difference
BABIP 0.000
HR/FB 0.000
HR/BIP 0.012
ISO 0.009
ERA-xFIP 0.000
Weak% 0.000
GB% 0.077

More horizontal movement correlates to slightly lower vsISO and HR/BIP values. From previous studies, there just isn’t going to be a high correlation. As expected, more horizontal movement correlates to more groundballs.


So in the end, I’ve found that three factors lead to weak contact

  1. High (popups) or low (groundballs) contact off the bat.
  2. Generating contact out of the strike zone.
  3. Horizontal movement on pitches.

For now, I could not find how changing pitch speed or being ahead in the count leads to weak contact. It makes sense that they do, but I have not unlocked the key just yet. In the next and final installment in this series, I combine the three factors to one metric to help figure out whose extreme batted ball stats are will stick or regress to league average.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR once, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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1 year ago

So basically it is vertical movement means swings and misses and horizontal movement means weak contact, right