This is probably the weirdest, most vague achievement in all of Batman: Arkham City. So don't feel bad consulting a guide to find it, I did. In order to get the 'Catch' achievement, you have to play a game of catch with your remote controlled Batarang.
To do this, you'll need to be at the place just after your first encounter with the Joker. You remember, the one where Batman has to jump out a window to avoid a bomb exploding. After your narrow escape, look up towards the ferris wheel. At the top of it is a shadowy figure. Throw your remote controlled Batarang at him, and he'll catch it.
- Xbox 360: 5G
- PlayStation 3: Bronze trophy