Setting a fair strike zone for every batter height

HostI was watching a game the other day and it struck me how weird the strike zone really is. It's this invisible box in the air that changes its size every single time a new person walks up to the plate. Most sports have fixed goals or hoops, but in baseball, the target moves based on who's standing there.

HostHow do we actually decide where that box starts and ends when every player is built so differently?

GuestIt's a bit of a moving target. If you look at the rule book, they try to tie the box to parts of the body so it scales with the player. The bottom is easy to find because it's just the hollow part of the knee. But the top is where things get tricky. It's defined as a line halfway between the top of the shoulders and the top of the pants. So, if a guy is six foot seven, he has a huge strike zone. If he's five foot five, it's tiny. The whole idea is that the pitcher has to throw to the person in front of him, not some fixed ghost in the air.

HostThat sounds like it would be a nightmare for the person behind the plate to keep track of. Wouldn't it be a lot easier if we just picked one size for the box and stuck with it for everyone?

GuestWell, if we did that, the game would probably break. Think about a really tall guy. If the strike zone was low and small for everyone, a tall pitcher could just throw down at his shins all day. The tall batter would've to reach way out of his comfort zone just to tap the ball. On the other side, a short batter would be getting walks all the time because the pitcher would've to throw over his head to hit a high box. The game stays fair because the strike zone is a map of where that specific person can actually swing a bat and hit the ball with some power.

HostBut even with those rules, umpires are human. They have to be guessing half the time. If a guy is crouching down low, does the box move with him, or is it based on how he looks when he's standing straight up?

GuestThis is a huge point of heat in the game. The rules say it's based on the batter's stance as he prepared to swing. So, if a guy squats really low, he can technically shrink his strike zone. Back in the fifties, a team actually put a person who was less than four feet tall in the game just to get a walk. He had a strike zone the size of a postage stamp. The pitcher couldn't hit it, and he walked on four straight pitches. After that, they made rules to stop people from making themselves look smaller just to cheat the zone. But even now, umpires tend to have a "mental" box that they use for everyone. They often miss the low strikes on tall guys and call high strikes on short guys because their eyes want the box to be in the same place every time.

HostSo we have these fancy cameras now that track every pitch. If the human eye is the problem, then the cameras should fix everything. If a ball crosses the line, the computer says it's a strike, and that's the end of it, right?

GuestYou would think so, but the tech has its own set of headaches. The cameras have to decide where a person's knees and belt are in real time. But think about what happens when a player moves. They waggle the bat, they shift their feet, and their jersey folds and ripples. If the camera is looking for the top of the pants to set the zone, a baggy jersey might fool it. If the jersey hangs down low, the computer thinks the strike zone is lower than it really is. We're finding out that the "robot" umps are only as good as the math we use to find those body parts.

HostThat seems like we're just trading one kind of error for another. Is the box even a flat window? I always see it on TV as a square over the plate, but the ball is moving in three dimensions.

GuestThat's a big part of the trick. The plate has depth. It's seventeen inches wide, but it also has that pointed back part. A pitch can be a strike if it touches any part of that three-dimensional space. A curveball might miss the front of the zone entirely but then drop in and nick the very back corner of the plate. To a human, that looks like a ball. To a computer, it's a strike. This is actually changing how catchers play. They used to try and "frame" the pitch by moving their glove quickly to make a ball look like a strike to the umpire. With a computer, that doesn't work. The computer knows where the ball was the moment it passed the plate, no matter where the catcher catches it.

HostIt feels like we're losing a bit of the feel of the game if we go all-in on the tech. There's something about the battle between the pitcher and the umpire that feels like part of the story.

GuestSome people love that tension, but players mostly just want it to be the same every time. The real goal of the new tech isn't to be perfect, but to be fair across the board. The big test now is how to track the jersey as it folds when a guy bends his knees, because even a small wrinkle can fool the computer into thinking the strike zone has moved.

HostThat batter standing there waiting for the pitch is really just hoping the eye in the sky sees his belt in the same place he does.