ESPN posts a good article on the progress of an automated ball-strike system (ABS). One takeaway is that robot umps have problems with the subjective dimension of strike zone height:

“There are two things you have to do,” Manfred told ESPN. “One is measure the track of the ball. We’re good there. The second thing you have to do is set the strike zone for each batter and we’re not there yet.”

Essentially, the league has two options: A height-based zone or a stance-based one.

A height-based zone is the simplest option: Players would be measured before each season and their strike zone would be set accordingly. Everyone at the same height would have the same zone, without taking into account the difference in stances for each player.

A stance-based zone revolves around camera readings of a player’s knees and hips as the pitch travels to home plate. The top and bottom would then be set based on a rolling median of the last 50 pitches seen by the batter — so hitters would not be able to get around the system by changing their stance depending on the count or situation in the game.

It’s a hard system to get right. This kind of zone would actually differ more from the current, human-umpire zone than the height-based approach would, forcing players to adjust in a more dramatic way.

ESPN.com

Players and fans in the minors like a challenge system where the call by the ump can be challenged with limits. I’ve thought for a while that machine should do what it does well, call the ball over the plate. Then the umpire can concentrate on the height dimension without worrying about the pate. I tend to get more upset at strikes off the plate and balls called over the plate that up or down. Let the machines make the concrete call and the humans make the subjective one.

Note that this would be a great way of training the machine as well. All of those calls should be fed back into the machine’s pattern recognizer, and after a while it may get very good at all the dimensions.