This is one of the simplest achievements to obtain. All you have to do is capture an enemy piece with your pawn, while a pawn is already on the tile. This can be done easily during the early game, as all or most of your pawns will be intact.
Play for the center of the board early on, as your opponent will do. Capture one of their pawns using one of yours and there will almost certainly be a pawn already on the tile you capture.