Batted ball insanity

Very cool stuff Harry (or should I say Matt?).

On the first set of balls, are the 1.6s and the 1.5s measuring the same thing? 

I’m assuming the first one is a timing to wherever Greene was standing and the second one is when the ball crossed the line into the outfield.  So to get an accurate comparison we’ll need to know where Greene was when he made the first play.

Unless he’s on the outfield grass when he makes that play it’s somewhat counter-intuitive that the harder hit ball takes longer to get where it was going. Is this due to the hops? Spin on the ball?

I’ve seen a lot of talk about the physics of fly balls and liners, but is there any way to model the physics of a ground ball?

After looking at the video of the Soriano and Johnson ground balls, I wonder if we are seeing the effects of batted ball spin ... in spite of the similar horizontal angles as measured by HIT f/x, Soriano’s ball ended up about 6 feet closer to 2nd (you can tell by the mowing pattern on the infield). Also Johnson’s ball seemed to bounce higher (and made contact with the ground fewer times?) than Soriano’s, so that it may have lost velocity less quickly, so that it could get through the infield faster in spite of a much slower initial velocity [assuming the HIT f/x measurement is correct].

Harry - I checked the MLB.com videos of all 4 balls as well.  On the Johnson ground ball the SS was playing further in than on the Soriano ground ball.  From the way the Johnson ball hopped it appears that he topped it and it hit the ground in the dirt surrounding home plate on the first bounce.  If that is so it is probable that Hit f/x had to few frames to calculate the speed off the bat and that what is given is the speed after the first bounce.  I talked to Greg Moore about this at the Summit and told him that when he did this it should be noted in the file somewhere.  I don’t think he realized that how much of the original speed would be absorbed by the impact with the ground.  So I think both balls were initially hit with about the same speed off the bat.  Johnson’s ball took one big hope and then skipped by the drawn in SS. Soriano’s ball was not topped as much, took several bounces before reaching the SS near the outfield grass and he just misplayed it.

The two balls hit in the air had much different spins.  Fontenot’s ball was sliced and undercut which caused it to curve more and stay in the air longer.  Soriano’s pulled ball was hit way out in front of the plate where his swing arc was rising.  It had much less undercut so it curved less and stayed in the air less time.  Since the perception of line drive and fly ball is governed not just by the initial angle off the bat, but also by the height the ball reached Soriano’s was really a line drive and Fontenot’s was really a fly ball.

Peter,

In his presentation, Greg Moore certainly indicated that HITf/x would report a misleading positive verticle angle and a slower speed for chopped balls they picked up only on the way up from the first bounce. In this case, since both ground balls were assigned downward angles, the vertical angle of the Johnson ground ball was measured on the way down to initial contact with the ground (which was near the edge of the circle of dirt surrounding the plate, as you suggest). I suppose it’s possible the velocity measure nonetheless could commingle frames before and after the bounce - did Greg say something to you personally to suggest that? This is worth a very close look to decide whether we can take the speed off the bat of these two balls as directly comparable. It would be surprising (to me) if the speeds off the bat are accurate and comparable, and yet the 73 mph ground ball could get to the infieder faster than the 98 mph ground ball.

@Joe
The energy of the bat is propelling the ball parallel to the ground (or a little upward).  The rebound of the ball off the bat is what creates the downward component of the velocity.  Because Soriano’s bat was moving faster at the point of contact than Johnson’s bat, in order to produce roughly the same initial vertical angle, he had to be on top of the ball a little more than Johnson.  This creates more topspin on the ball hit by Soriano.  That would make the Soriano ball bounce lower on at least the first bounce and consequently hit the ground more often on its way to the shortstop. 

According to my bat-ball collision model, the Soriano ball had about twice as much topspin as the Johnson ball, about 1100 rpm vs. 500 rpm, created by an offset between the center of ball and bat of about -.67 inches for Soriano and -.54 inches for Johnson, generated by a bat speed at point of contact of about 59 mph for Soriano and 29 mph for Johnson.

Both balls also had significant sidespin, ~2500 and ~1900 rpm, but the sidespin shouldn’t affect the bounce much and 1.5 seconds isn’t much time for the sidespin to affect the trajectory in the air.

@Harry
I missed the ground ball spin discussion at the summit, but my own experiments with bouncing a rubber ball on a tile floor do show that the ball loses much of its spin after the first bounce.  A baseball on grass/dirt would probably experience more friction and lose even more of its spin when it bounced.

Peter, agreed about the desired resolution, but I am not sure about HITf/x using the “mirror image” of the angle after ground impact, since there are ground balls in the april data with large positive vertical angles [like plus 50-60 degrees - just like a fly ball] and very slow speeds off the bat [like 20 mph]. I looked at several of these on video, all chopped nearly straight down. Definitely no adjustment to the mirror angle on those balls ...

Harry - This site lets you change Magnus force and shows you its affect on the trajectory and the distance.  Unfortunately it doesn’t give you the time to that distance.  But time is directly proportional to maximum height.  You don’t mention what distances Matt had for these two hit balls.  My translation of the Gameday hit locations has them only a foot apart at arouond 240 feet where they were caught.
http://faculty.tcc.fl.edu/scma/carrj/Java/baseball4.html

@Greg

good point. From the fielder perspective it isn’t _as much_ how the ball got there, but when it got there. I’m still intrigued by the hop characteristics, though.

I can’t help but think judging and handling different hop types is a skill, and that where the fielder got the ball relative to their normal throwing position has an impact on converting a fielded ball into an out.

Caught on heels vs. charging the ball, etc etc

@Peter:  Interesting “before/after” analysis you did of a grounder.  Carrying the analysis a bit further, the normal (vertical) component went from 11.8 mph before to 6.4 mph after, implying a COR of 0.54, more or less what I would expect.  The horizontal component went from 94.8 to 77.4.  If the fractional loss in velocity were the same for horizontal and vertical components, then the “mirror” prescription would be correct.  However, you can seen that there is a much larger fractional loss in the vertical direction, so that the bounce angle (relative to the ground) will always be less than the initial angle.  That is exactly what the data shows.  For a ball hit with topspin (and most grounders are), it will always be the case that the bounce angle will be less than the initial angle.

It would be very interesting to see more analysis of this type.

@Peter - here are the fielding locations for the two outfield flies

Definitions from Matt:
x  
feet off the third-base foul line, along x-axis

y
feet off the first-base foul line, along y-axis

r
feet from home plate = sqrt(x^2 + y^2)

theta
angle off 1B foul line = arctan(y/x)

Fontenot
59, 227, 234, 76

Soriano
60, 241, 248, 76