Seeing the opponent was off guard, the boxer landed a knockout punch.乘对手不提防，那拳击手一下子把他击倒了。Seeing the opponent was off his guard, the boxer landed a knockout punch.乘对手不提防，那拳击手一下子把他击倒了。They've been bluffing, trying to keep him off guard.他们一直糊弄他，设法使他不提防。