Explaining how a baseball player catches a ball

NCBI ROFL: How baseball outfielders determine where to run to catch fly balls.
[Via Discoblog]

fly ball

“Current theory proposes that baseball outfielders catch fly balls by selecting a running path to achieve optical acceleration cancellation of the ball. Yet people appear to lack the ability to discriminate accelerations accurately. This study supports the idea that outfielders convert the temporal problem to a spatial one by selecting a running path that maintains a linear optical trajectory (LOT) for the ball. The LOT model is a strategy of maintaining “control” over the relative direction of optical ball movement in a manner that is similar to simple predator tracking behavior.”


Photo: flickr/SD Dirk


Being a ball player for so long, I remember a lot about this area of research because this was the first paper that actually seemed to explain how an outfielder actually caught a fly ball, rather than propose a strategy that was not really being used by anyone with real experience.

Catching a fly ball is not easy and takes a lot of practice. There had been papers earlier that looked at how this might be done. But there were several real flaws in the them, particularly for people who were real ball players.

One of the flaws was that they could not really give a good explanation for how someone could be moving towards a moving ball and time the catch to happen while still moving. They predicted that a stationary position would be best for catching a fly ball. The explanations were fine for a ball hit directly at someone where they essentially moved in a forward or backward track. But even good ball players will say that tracking these sorts of balls were much hard than any other and did not really fit how they found a ball.

And this approach could not explain how a player could simultaneously run towards where the ball would be and catch the ball, all while still in motion. It required the player to stop, track the ball, move, stop, track the ball, etc. It did not really explain how a player could catch a ball while at a full run to the side. In fact, as I recall, this would be an impossible task under this older model. While earlier research found that this approach was used by many inexperienced players , it is not what was seen with experienced players.

This was the first paper that actually addressed how a player could simultaneously run, track and catch the ball, all with relatively simple, easily understood math. In fact, the strategy works best when the player continually moves to the ball, timing his catch to where the ball is, rather than run real fast to the spot and then wait. It explained why it is actually easier to catch a ball while on the run than when simply stationary.

I know personally that I can get a pretty good idea of where a fly ball is going as soon as it is hit. I know if it is over the fence, close to the warning track, or just a little blooper. I have to see the batter. In fact, I would move around on the field to be able to see the actual swing, etc. If I was blinded by a base runner standing in the way, it was much hard to follow the ball.

And, often a ball player can start a run after seeing the initial flight without having to see the ball at all. Then he can turn and track the ball. So I think there is some experience level here that permits a player to make an initial judgement of where the ball is headed, an initial judgement that is often pretty accurate.

But the LOT strategy really seems to explain how adjustments are made to get to exactly where the ball will go, how to deal with perturbations in the flight due to wind, etc. and make the catch. It was nice to see something like this published in Science that actually seemed to accurately explain how it worked for me.

2 thoughts on “Explaining how a baseball player catches a ball

  1. Is this a learned behavior? Or an instinctive one? The latter would explain why pro players stand out even at an early age.

    1. The hypothesis is that it is an adaption of the same ability of a carnivore to track and catch the food it is chasing. They move to where the prey is going and the prey tries to escape by changing that trajectory. Notice how dogs chase Frisbees in a similar fashion – that is, they can get to the Frisbee on a dead run rather than run and wait.

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