Hand signals are commonly used in baseball to surreptitiously communicate intent to teammates without giving away your strategy to opponents. I think what GP was getting at is that this technology could be used to automate the reading of hand signals. I'm not sure it would be effective, as the pro baseball players are already quite sophisticated at both reading and obfuscating hand signals, at least at the highest levels of the game.
Genuine question, I don't know how baseball works.