Re: http://www.chess.com/livechess/game.html?id=235253530
See here http://www.chess.com/learn-how-to-play-chess.html
En Passant
The last rule about pawns is called “en passant,” which is French basically means “in passing”. If a pawn moves out two squares on its first move, and by doing so lands to the side of an opponent’s pawn (effectively jumping past the other pawn’s ability to capture it), that other pawn has the option of capturing the first pawn as it passes by. This special move must be done immediately after the first pawn has moved past, otherwise the option to capture it is no longer available.
I don't get why this is not a checkmate:
Am I missing something?