With the scores tied at 20, Jeff Fisher's Rams held the ball, and planned to run out some more clock before kicking the game-winning field goal. That was the plan, at least.
With 2:38 remaining, the Rams would have to run only one more play before the two-minute warning. But a mistake by the clock operator froze the clock for a few seconds, thereby forcing the Rams to run two plays before the 2:00 mark.
This, essentially, gave Matthew Stafford and the Lions an extra timeout. They then marched down the field and Stafford passed to Kevin Smith for the game-winning touchdown with 10 seconds remaining.
Coach Fisher was frustrated, but conceded, "There was an error, I did report it to the league, and that's all I can do."