Does Movement Influence BABIP?

A couple weeks back, Pizza Cutter found an interesting oddity in that Troy Percival had consistently posted very, very low BABIPs. In response, Dave Studeman brought up Mariano Rivera–another pitcher with consistently low BABIPs–and how it has been somewhat proven that elite relievers can register atypical results with this statistic. Mentioned on a few other sites was the idea that movement may be a central cause for these lower batting averages on balls in play; due to said movement, the sweet part of the bat would fail to meet the ball as it normally would on more “standard” pitches.
Last week, we explored the relationship between fastballs 92+ mph and BABIP, examining how it differed at each mile per hour interval. 92 mph to 96 mph clocked in between .290-.310–the established general range of BABIP for pitchers–before dipping to .273 at 97 mph and shooting back up to .293 for all thrown 98 mph or higher. The 97 and 98+ groups were too small in their sample sizes to definitively fail the 5% hypothesis; we would need around 1,650 balls in play and, combined, had 1,032. Still, the combo of 97 and 98+ offered a .279 BABIP, perhaps suggesting that the .293 at 98+ was the anomaly, not the .273.
Today we will look at the movement within the same 92+ mph range in order to attempt to answer the question posed in the title. First, though, a pre-requisite of sorts with regards to movement: the relationship between horizontal and vertical components is not extremely known yet other than some telltale signs aiding in the classification of pitches. For instance, a two-seam fastball will have much higher horizontal movement than vertical movement; however, four-seam fastballs generally have lower horizontal movement and higher vertical movement.
I queried my database for all fastballs 92+ mph and separated the results into groups by movement rather than velocity intervals. The signs (+-) were reversed so that righties and lefties could be grouped together as well. First, here is a sample size grid of sorts, showing all balls in play for each horizontal group and vertical subgroup; note that the subgroups differ for each horizontal movement grouping so they will be called simply below average or above average as they were essentially determined by the average or a similar type of cutoff point. The reasoning for this is the aforementioned relationship between movement components; for fastballs, lower horizontal movement will usually correlate with higher vertical movement with the inverse also being true.


Below Vert BIP

Above Vert BIP

0-4 in



4-8 in



8-12 in



12+ in



BABIP takes a while to stabilize, moreso than many other statistics, so I wanted to have at least 2,000 balls in play for each sub-grouping, preferably more. From 0-12 inches of horizontal movement we have large enough samples to notice discrepancies. Greater than 12 inches, however, offers just 743 balls in play. While I definitely plan to explore this and the velocity articles later in the year when more data is available, for now, I am going to exclude the group with more than 12 horizontal inches.
Looking at the other three groups and their two subgroupings each, here are the Ball%, Strike%, HR%, and BABIP:











































The percentage of balls essentially stays in the same general range while the strikes fluctuate. The subgroupings with above average vertical movement have much higher strike percentages than others. So, judging by this it seems before we even get to BABIP, that higher vertical movement in these larger groups result in a higher percentage of strikes.

The BABIPs for horizontal movement groups with below average vertical movement register: .289, .302, and .315. The BABIPs for horizontal movement with above average vertical movement clock in at: .286, .292, .298. Judging from these results it would appear that, yes, movement does have some type of effect on BABIP. Each horizontal group posted higher counts when they had below average vertical movement, and at every interval as well; .289 to .286, .302 to .292, and .315 to .298. Additionally, all pitches 92+ mph with 0-4 inches of horizontal movement, regardless of whether or not they fell above or below the vertical cutoff point, produced a BABIP lower than .290, which is generally the lower edge of the .290-.310 range we expect it to fall into.

Tomorrow I’ll come right back with the total number of unique pitchers and those comprising at least 1% and at least 5% of the sample, in order to see if the results are skewed in any way. For now, though, it appears that, regardless of your horizontal movement, having above average vertical movement will produce a lower BABIP at each horizontal interval.


11 Responses to Does Movement Influence BABIP?

  1. Pizza Cutter says:

    Wonder what these data would look like in a binary logit regression.

  2. dan says:

    Don’t we all?

  3. dan says:


  4. John, thanks. I actually didn’t compare the vertical movement to the flyball % though I’m sure I’ll find the higher the vertical movement the more flyballs which would definitely confirm the lower BABIP. Yeah, I’ll run a binary logit and see what I get.

  5. John Walsh says:

    Good stuff.
    A couple of things stand out: 1) more vertical movement means lower BABIP. I think this is just the statement that more vertical movement means a higher fly ball percentage, which means lower BABIP. We knew this, but it’s good to see you confirm it.
    2) Within the two vertical movement sub-groups, you see a positive correlation between horiz movement and BABIP. But, I’m wondering if that might also be a manifestation of the same effect, since there is a correlation between horiz and vert movements. In other words, even within your below-average vert movement sub-group, there may still be a horiz-vert correlation which leads to the BABIP pattern that you see.
    Pizza is right — you could probably benefit from a regression analysis here.

  6. Dave Evans says:

    The first thing I noticed is that it is going to be almost impossible to justify any cause and effect conclusions with this study because of you do not account for speed. First you probably want to check if speed correlates with movement. If it doesn’t, you could be okay, but if it does that could mean that we are just seeing vertical movement as a side effect of speed. I would advise adjusting for speed in almost any observational study with pitch f/x, as it could confound with the movement, control, and overall mindset of the hitter (swinging less at a hard thrower). Pitch f\x is awesome, but it is just a big observational study, so we need to be careful with any conclusions drawn and the best way to do that is to adjust for as many variables as possible, especially speed.

  7. Dave, as I mentioned (I think I did at least), there is not yet enough data to have large enough samples with further subgroupings.
    Of course I would love to do a similar breakdown as my fastball article going mph by mph, or at least in shorter ranges, and then compare the movements, but that might not happen until around mid-August if not later.
    As I also mentioned in here, the pitchers with higher vertical movement are the ones who throw four-seamers, which are more often than not thrown harder than the two-seamers.
    So, yeah, you’re right, but as an intro to what could be looked at in the future, it does appear that, in some way, shape, or form, the movement does have an effect on BABIP. We could eventually find that it is strictly due to the velocity but there is definitely something here.

  8. Isaac says:

    I may be wrong with this assessment, but when John says that the high vertical movement generated lower BABIP is pretty much synonymous with higher fly ball rates, couldn’t the lower BABIP’s be a result of just weaker contact? As the strike rate, and presumably the swing and miss rate, rises with increased vertical movement, would it be a stretch to say that weaker contact is also made more often on both ground balls and fly balls? I am relatively new to advanced metrics and I realize I may be making a few leaps and faulty assumptions, but am I way off base with this one?

  9. I don’t think you would be entirely off base but the fact is we don’t really have anything to measure your theory. When the Hit F/X system is revealed, which would offer the bat speed, how hard it was hit, etc, we could really determine if movement affects the magnitude of contact, and then plug it back in here into some regression to see if ultimately movement affects BABIP and if it does so because lesser contact is being made.

  10. Isaac says:

    Thanks for the quick response. Oh, and good stuff. This article was extremely interesting.

  11. Isaac, thanks. You might also enjoy the article I did the week or two before this, two of them actually, titled “Breaking Down the Heater” and “Heater Getting Hotter.”
    They both explored how velocity on fastballs affected BABIP, going from each mph interval 92+. So, looking at the BABIP of all 92 mph fastballs, 93 mph, 94 mph, etc.
    Around the beginning of August I’m going to revisit both of these to ensure large enough sample sizes and see what we get.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: