There’s a computer system that’s able to tell whether a pitch is in the strike zone or not. The umpires’ union is not into the idea of using it in games, and MLB hasn’t allowed it yet. But the system has existed for a while, and at some point about ten years ago, a bunch of dweebs realized that as long as MLB wouldn’t simply use that computer in games to call balls and strikes correctly, the dweebs could use it to quantify which catchers are the best at getting umpires to do their jobs badly. This was a major advancement in the long-time understanding that some catchers are able to fool umpires to the benefit of their team, some are not, and some actually fool umpires to the detriment of their team.