Had the exact same thing happen to me yesterday. Had a pretty good streak going, and after being creamed all game, it looked like my team had a chance to hold the final objectives. Then the game froze, needless to say, I was PISSED. I heard that Metro and the Aftermath maps all have a tendency to freeze, especially with the HD content installed, something about putting too much stress on the console? Just what I heard, can't say for sure what would cause it :/