Bat Meets Ball: Checking in on the HitF/X data
To begin with I want to say great work to all my colleagues here on their draft coverage. The interviews they all posted were first rate, Marc's coverage has been exhaustive and Marc and Rich's liveblog was a perfect way for me to follow along with the first round. So great work team.
The draft was probably the most exciting baseball event of the past week, but a not too distant second, for some of us, was the release of the first batch of hitf/x data. This is the analogous data for batted balls that pitfchf/x gave us for pitches. Like pitchf/x it is captured by two high speed cameras at each stadium. Based on pictures of the ball just as it is struck by the bat and fractions of a second afterwards the batted ball's initial speed and trajectory are estimated. For a technical discussion about how this is done and the accuracy of the method check out this post at Tango's and MGL's Inside the Book blog.
This first release of hitf/x data covers all batted balls from this past April and gives the speed of the ball just it leaves the bat and its vertical angle (or launch angle) and horizontal angle (or spray angle). Analysis of this week-and-a-half old data has already poured in. Ryan Howard crushes the ball. The optimal vertical angle to hit the ball at is around 11 degrees (with 0 degrees being parallel to the ground). David Ortiz is in trouble, balls came off his bat at the same speed as balls of the bat's of Alexi Casilla and Endy Chavez.
It has been a little while since I have had a really nice heat-map heavy visualization post and I thought this data would be a great opportunity to rectify the situation. Since there is only one month of data available the heat-maps presented here are more 'smoothed' than ones I have presented previously. For this reason I am not 100% comfortable about the conclusions at the outer edges of the images. But in and around the strike zone, where there have been lots of hits, I think the results are good.
Vertical angle of a hit based on pitch location
First off let's look at the average vertical angle of a batted ball based the location in the strike zone where it was hit. We know that hit balls with a low vertical angle tend to be ground balls and pitches lower in the zone are hit more often for ground balls. Thus, we should expect that pitches down in the zone are hit for a low vertical angle. Is that the case?
The vertical angle ranges from 90 degrees (popped straight up), to -90 degrees (driven straight into the ground), with a zero degree hit being parallel to the ground. Also remember that the images are from the catcher's perspective, so negative x-values are inside to RHBs and positive x-values inside the LHBs.
As expected the lower in the zone the lower the vertical angle of the average hit ball. In opposite-handed at-bats there is an additional trend for away pitches to have a lower vertical angle off the bat. So pitches down-and-away are the most likely to be groundballs and pitches up-and-in are the most likely to be fly balls and pop ups. In same-handed at-bats this inside-outside trend is much weaker and the gradient is largely just based on vertical location of the pitch.
Horizontal speed off bat based on pitch location
The initial speed of the ball off the bat is not as important in determining the success of a hit as the initial horizontal speed. A hit popped straight up very fast is just as bad a hit popped straight that is a little slower off the bat. On the other hand, the horizontal speed (the speed of the hit in the horizontal plane) is important in determining how hard a ball is to field and how far it goes. So below I plot the average speed of a hit ball in the horizontal plane (in mph) versus pitch location. Based on my HR heat maps I expect the highest speed hits to be slightly up-and-in.
Wow, that is the opposite of my assumption. The peak speed is up-and-away, and far up-and-away. There is a large peak speed out of the strike zone. The area of high speed hits extends from up-and-away to down-and-in through the strike zone. This is actually the same trend we previously saw with the highest run value of contacted pitches. Remember this is just based on batted balls, so there could be something of a selection bias. Maybe the only pitches up-and-away that are swung at and hit get crushed. Still this result is very surprising to me.
Peter Jensen made the following comment:
Here is the total speed off the bat by pitch location.
Just as Peter suggests this pulls the location of fastest balls off the bat closer to the batter and up. It is still slightly outside, but not far outside like before. The area of high horizontal speed hits down in the zone were, not surprisingly, slowish in total speed.
End of Edit
The next couple of weeks will be very exciting as this new wealth of data is examined. It affords a novel way to examine questions about baseball, and a potentially valuable tool to evaluate batters. If you have any general questions about the hitf/x data or any specific questions you think the data could answer feel free to post them in the comments. Also, make sure to check out Mike Fast's and Harry Pavlidis' early work with the data that I linked above.
What proportion of horizontal speed is determined by the velocity of the bat, as opposed to the quality of contact? The bat head is moving faster than than the handle, so we should expect a broader diagonal concentration as we see in these graphs, rather than a more circular pattern concentrated within the strike zone.
Posted by: Grunthos at June 11, 2009 6:54 AM
Good point about the velocity of different parts of the bat, I hadn't thought about that. I know that Mike Fast is working on a model to describe the bat-ball collision that I think would address your question. I have not seen any results from it, I don't think he has made them public yet.
Posted by: Dave Allen at June 11, 2009 8:01 AM
I'm gonna go with much longer moment arm and more directed force generating higher torque on the up and away pitches leading to higher velocity. When a hitter has to pull his hands into the body to hit an inside pitch, the elbows, shoulders, and wrists aren't as involved as on away pitches, and they're frequently moving in a different direction than the eventual path of the ball, so both the velocity of the bat head and the direction of the force propelling it are not ideal for transferring max energy to the ball.
Posted by: Hunter at June 11, 2009 8:26 AM
Regarding bat speed and such things, there are really two issues involved. First, the bat speed is larger the closer you are to the tip of the barrel. On the other hand, the "collision efficiency" (i.e., the ability of the bat to transfer energy to the ball) peaks about 7 inches in from the tip. So, when you put it all together, you expect the maximum batted ball speed to be around 5" from the tip. This is pretty much confirmed in lots of ways, including computer simulations of the bat-ball collision, laboratory measurements of the collision efficiency along different points of the barrel, and high-speed video that is able to measure batted ball speed as well as the impact location.
Posted by: Alan Nathan at June 11, 2009 9:51 AM
In opposite-handed at-bats there is an additional trend for away pitches to have a lower vertical angle off the bat.
This seems like the wrong conclusion to me. The away pitches look the same in opposite handed at-bats as for same-handed. The difference is inside pitches get hit with higher angles on opposite-handed at-bats than same-handed ones.
It also looks like opposite-handed balls get hit with lower horizontal velocity all-around, but especially on inside pitches (not surprising, they have higher angles and thus lower horizontal velocities).
Posted by: LarryinLA at June 11, 2009 10:33 AM
Dave - I think you may want to choose actual SOB to graph instead of horizontal SOB. Balls hit with a greater vertical angle will have a smaller proportion of their speed as a horizontal component. A batter hitting a high inside fastball is almost forced to hit it in the air because he is hitting it during a portion of his swing where the bat angle has the head above the handle. That portion of the swing also is near the maximum swing speed so the batter will be trying to undercut the ball slightly to raise the vertical angle of the ball off the bat even more and maximize his distance and the possibility of a home run. So the batter is sacrificing horizontal speed off the bat to gain maximum hit ball distance
A batter hitting an outside high fastball. Will be doing just the opposite. His bat angle still has the head lower than the hands causing a lower vertical angle. Most batters should be trying to hit the ball as a line drive to the opposite field since their chances of hitting a home run a relatively small and a line drive to the opposite field maximizes their run value. It also lowers the overall vertical angle of the hit ball and maximizes the horizontal component of the total speed off the bat. That is why your second set of graphs look the way they do. Change from HSoB to SOB and they should look very different. Love the graph images by the way.
Posted by: Peter Jensen at June 11, 2009 11:03 AM
Thanks, that is great information to know relative to this work.
Yeah I guess that I meant in opposite-handed at-bats outside pitches have a lower vertical angle than inside pitches in opposite-handed at-bats. The way I wrote it originally did make it sound like outside pitches in opposite-handed have a lower angle than outside pitches in same-handed at-bats. The way you explain it is clearer than how I did.
Great point. See edit in body of post.
Posted by: Dave Allen at June 11, 2009 1:04 PM
Dave - Thanks for giving us the new graphics. They probably illustrate why the fences are put farther away in center field!
Posted by: Peter Jensen at June 11, 2009 6:29 PM