I'm guessing these are baseball terms, I know nothing of baseball.
You could probably just as easily Wiki it, and if you didn't then it probably means you don't really care to know what I'm about to tell you ^^; , but fyi may as well since it's simple to translate:
the pitcher is the guy who throws the ball towards the batter, and the catcher is the guy who squats down behind the batter to catch the ball in case he fails to hit it. The idea, thus, is that the pitcher is the one who puts out while the catcher is the one who receives.
Aside: "to pitch an idea" is to try to persuade somebody that a particular idea is a good one. "Pitching" is thus an American English verb which implies delivery.