I told Mike Nickeas about this article on Baseball Prospectus, then we talked about it.

One of the most interesting parts of the conversation actually came after we stopped filming. Jay, one of our video guys, asked Nickeas why an umpire wouldn’t just look at the ball (not the catcher’s movements). Nickeas said the ball’s often coming so fast that if you blink you miss the spot where it crossed the plate, so lots of movement from the catcher would be enough to sway the umpire’s judgment.

He also noted that umpires talk amongst themselves during games, so catchers need be careful about trying to pull balls back in the strike zone. If they’re too obvious with it, the second-base umpire will tell the home-plate guy and the catcher might lose some of the borderline calls. Plus, there’s a good chance said second-base umpire will be behind the plate later that series.