It is a play that will haunt the New Orleans Saints and their fans for a long time. They needed one stop against the Minnesota Vikings. They needed to tackle a defenseless wide receiver in bounds. Do that, and they would be headed to the N.F.C. Championship. But caught up in the moment, a rookie missed a tackle, and it cost his team everything. Here is what went wrong:

The Setup

It was 3rd-and-10 at Minnesota’s 39-yard line. There were 10 seconds remaining, the Vikings had no timeouts, and New Orleans was clinging to a one-point lead. A play of any kind that did not get out of bounds would almost certainly end the game, since the Vikings would not be able to stop the clock in time to try a game-winning field goal.

“We knew that all we needed was a field goal,” receiver Adam Thielen said. “Obviously, we knew it was going to be tough because all they had to do was stay back and not give up the big play. I don’t think anybody in the huddle was down. We were just trying to make a play.”