system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do catchers in baseball give the pitchers signals?

What do these hand signals mean? Shouldn't the pitcher know what pitch to choose?
gpt
The pitcher and the catcher usually work out in advance a general strategy, so in most cases the catcher is simply *confirming* what kind of throw to expect. The pitcher will sometimes shake a signal off, which tells the catcher "no, try something else." The pitcher makes the ultimate call, but it's up to the catcher to offer suggestions.

>Catcher: "Are we doing this?"

>Pitcher: Shakes his head "no."

>Catcher: "How about this?"

>Pitcher: "Yes."

>Now the catcher positions himself properly for the expected pitch.

The catcher might also give a signal which basically says "Hey, this isn't coming from me. The pitching coach is telling us to do this pitch against this batter."

The catcher is *behind* the batter, so he is in the best position to do this secret signalling. If it were reversed, then the batter would know what to expect.

When there are runners on base they sometimes use a more subtle signalling method. This is where that general strategy meeting that took place before the game comes in.