I don’t know about you, but I continue to enjoy MLB’s new statcast technology. If you have read a few my articles, you’ve probably already noticed. When looking at a hitter’s performance, I often utilize Exit Velocity (the speed at which the ball leaves the bat) and Launch Angle (the angle at which the ball leaves the bat).
Using both, Statcast can provide the average value of a batted ball at any specific combination of those two. Thus, BaseballSavant.com - the site that hosts MLB’s statcast data - has a stat called xwOBA. That stat replaces the on-contact portion of wOBA with the average value of each player’s batted balls. xwOBA is more predictive of future wOBA than actual wOBA, so it’s become a convenient thing to check when a hitter is on a hot streak.
One seemingly glaring thing that xwOBA ignores however, is player speed. The faster a player runs, the more likely he is to leg out an infield hit. That player can also more easily turn singles into doubles and doubles into triples. Craig has already shown that Speed plays a role in both base-running and defense. Speed also plays a role in hitting performance, even if it’s not that large.
Statcast has us covered here too, with their Sprint Speed leaderboard. Sprint Speed is defined as the player’s “fastest one-second window”, and is measured in terms of feet per second. For more on how it’s calculated, check here.
However, speed doesn’t affect every batted ball equally, and for that we’ll turn our attention back to Exit Velocity and Launch Angle. Baseball Savant groups all batted balls into six different categories based on the two, called the six qualities of contact. To better illustrate this, here is Magneuris Sierra’s radial chart:
The protractor-shaped image above is used to visualize any batted ball in terms of Exit Velocity and Launch Angle. Each dot is one of Sierra’s batted balls in 2017. The six colored regions represent the six qualities of contact, and they are listed on the side.
Barrels and Solid Contact are hard-hit balls in the air. Maybe speed adds value in those categories by turning singles into doubles and doubles into triples. Flares and Burners are bloopers and hard hit grounders. Perhaps hard hit grounders offers some extra base hit ability, if placed right. The effect is probably small though. Under contact is pop-ups and medium velocity fly balls. Speed has very little to decide there.
Topped batted balls are different though. Those are essentially either low-angled grounders, weak grounders, or those with some combination of both traits. These are typically the ones I think of when I think about speed playing a role. Those take longer to reach the infielder than hard hit grounders, lowering the margin for error that he has to make the play. Fast runners can turn these into hits. Weak contact - which is any batted ball under 60 MPH - could also play a role, but happen much less frequently.
So we’ll start with looking at topped batted balls. We’ll utilize each player’s xwOBA minus their wOBA on topped batted balls, as well as each player’s Sprint Speed. 380 players both appeared on 2017’s Sprint Speed leadership and had more than 20 topped batted balls in 2017. Here’s a scatter plot:
There’s an r squared value of .23 here. A player’s speed can explain some of a hitter’s ability to over-perform topped batted balls. To be honest, most of the rest is probably good placement and good ole’ randomness, both of which probably aren’t repeatable. Maybe handedness plays a role. Perhaps first step speed could be a factor.
This is by far the highest r squared for any quality of contact. Weak contact has a .12 r squared value, but comes with just a sample size of just 34 players with more than 20 batted balls in the “weak” category. In third place was Solid Contact with a .03 r squared value.
Some would say .23 is a low score, but we are talking about some pretty low thresholds here. Baseball offers a lot of randomness over 20 at-bat intervals. What’s important is if this stat improves over regular xwOBA. For the same player pool, here’s each player’s wOBA and xwOBA on topped batted balls:
Despite xwOBA being more indicative of future wOBA than wOBA itself, the relationship between current wOBA and xwOBA on topped batted balls is pretty weak over this small of a sample. The r squared score here is just .06.
Now we’ll use the best fit line in the first scatterplot. When applied to a player’s speed, the equations gives you what we’ll call xGap: the expected difference between a player’s xwOBA and wOBA on topped batted balls.
So for each player, we’ll apply their xGap to their xwOBA on topped batted balls, and call that their new Topped xwOBA. Then, we’ll compare that to their actual wOBA on topped batted balls:
The r squared value here is .28, a marked improvement over just using xwOBA. That to me is what’s important. We already know xwOBA is more reliable than actual wOBA, when projecting future performance. However, player speed was a missing variable. Of course Dexter Fowler is going to get more out of his grounders than Yadier Molina. But what type of difference are we looking at? That’s what I wanted to know.
So let’s look at the Cardinals that were part of the sample. Unfortunately, Magneuris Sierra didn’t make the Sprint Speed leaderboard. That’s unfortunate, because he’s basically the inspiration for this article. For all those that did, here’s their Sprint Speed along with their xGap:
Cardinals sprint speed and xGap
Tommy Pham is the Cards’ fastest runner according to statcast, and Yadier Molina is the slowest. No big surprise there. It is however, suprising that Jose Martinez grades out as an above-average runner (average is 27 ft/second).
That gives the Cardinals two well-above average runners: Pham and Dexter Fowler. They have three slightly above-average runners in Randal Grichuk, Aledmys Diaz, and Paul DeJong.
On the other end, Jedd Gyorko, Matt Carpenter, and Stephen Piscotty join Yadi as well-below average runners. That leaves Kolten Wong, Greg Garcia and Martinez as slightly above-average performers.
Looking at the league extremes, fastest runner in the league Billy Hamilton has an xGap of .070 points. On the other end, Albert Pujols is at -088. In other words, Pujols is slower than Hamilton is fast. Foot injuries suck.
This is just topped batted balls though. We’re trying to assess speed’s ability to create base hits on the whole profile. To do so, I’ve found the percentage of each player’s plate appearances that ended in a topped batted ball. I then multiplied that by their xGap, to find how speed should be able to help or hinder their profile:
Speed's effect on total xwOBA
|Player||Topped%||xGap||new - xwOBA|
|Player||Topped%||xGap||new - xwOBA|
In prior posts, I’ve used Topped% to refer to topped batted balls as a percentage of batted balls. Here, it’s topped batted balls as a percentage of plate appearances.
The results here show that speed does have an effect, but it’s not very strong. Tommy Pham’s speed should creates additional base hits, but only to the effect of .009 points of wOBA. Maybe weak contact adds a point or two. That only comes about to about 3 points of wRC+. On the other end, Yadier’s lack of speed costs him about 4 points of wRC+.
Interestingly, Carpenter’s propensity to either walk or put the ball in the air mitigates the penalty he sees from his slow speed. There’s the issue of shifts, which also handicaps Carpenter. We’ll try to measure that another day though.
I’m not sure where Sierra would rank in terms of speed compared to these players. I’d guess he’s about as fast as Pham. While it’s a small sample, more of Sierra’s batted balls have been of the topped variety, so maybe speed could be responsible for 5 or 6 points of wRC+. Over 600 plate appearances, that’s somewhere between 1/3rd and 2/5th of a win.
There are very slight advantages to other batted ball types, but only weak contact is influenced by speed at least half as much as topped batted balls. The league average rate of topped batted balls compared to all batted balls is 36%, compared to just 3.8% for weak contact. Solid Contact comes in a distant third in terms of being influenced by speed. That is probably where speed turns singles into doubles, and doubles into triples. However, Solid Contact only counts for 5.1% of batted balls. Only topped batted balls occur frequently and have a significant effect on speed.
Don’t get me wrong, this doesn’t mean fast hitters should be trying to hit topped batted balls. Billy Hamilton’s xGap is .070 points, and the result is a .227 new xwOBA on topped balls. That’s significantly below the league average, whether going by on-contact or all plate appearances. It’s a nice to have when a hitter does top the ball though.
Working in the other direction, it’s all the more reason for Carpenter and Molina to work on getting the ball in the air more. Carpenter has been doing that for years at this point, and Molina’s starting to do the same, at least in situations that call for it. The effect however, isn’t one that makes or breaks a guy at the plate. It’s a very marginal upgrade or downgrade. Most of hitting performance is based on, you know, the hitting. It’s nice to have an idea of how much of it has to do with speed though.