The Detroit Lions lead the New Orleans Saints 14-7 in the second quarter, but it could have been a 21-7 lead, had an over-zealous referee blew a whistle too early, something they've been doing all season. Late in the second quarter, the Lions forced their second fumble of the day when Willie Young hit Drew Brees while he was attempting a pass in Lions territory, and forced the ball out of Brees' hands and onto the ground, where Detroit recovered it, and started to return it, when they heard the whistle.
It was very clearly a fumble, as Brees' hand didn't come forward at that point. The problem is the whistle, which negated a potential return and big play for the Lions, who are huge underdogs in this contest. Detroit took over instead, but were unable to get anything done on the drive, quickly being forced to punt.
Below, we've got a video of the fumble and the whistle.