The NFL's new overtime rules are an odd mix of the regular season rules (sudden death) and the college rules (each team gets a possession). The momentum to make the switch came when the 2009 NFC Championship game between the Vikings and Saints went into overtime making some scramble to avoid a situation where a team could go to the Super Bowl on a one possession overtime.
So the owners made the switch last May and this is the first time we're testing it out. It's called modified sudden death and the key to remember is that the league decided on these rules because they wanted to avoid a one possession overtime in the playoffs where a field goal ends the game. That's what the new system attempts to avoid.
Here's the technical definition of the new overtime rules:
Each team must possess or have the opportunity to possess the ball unless the team that has the ball first scores a touchdown on its initial possession. Play continues in sudden death until a winner is determined, and the game automatically ends upon any score (by safety, field goal, or touchdown) or when a score is awarded by the Referee for a palpably unfair act. Each team has three time-outs per half and all general timing provisions apply as during a regular game. The try is not attempted if a touchdown is scored. Disqualified players are not allowed to return.
Here are a few additions points and clarifications:
Each team is guaranteed a possession, or the opportunity to possess, if a touchdown is not scored on opening possession. So if a team takes the overtime kickoff, drives down the field and kicks a field goal, the game is not over. They will now kickoff to the other team who can kick a field goal to tie it and turn it into real sudden death, turn it over to end the game or score a touchdown to win the game. If the team that gets the ball first takes it down and scores a touchdown, though, the game is over.
Other ways to win the game. When we're dealing with possession or the opportunity to possess there are a few quirky ways to win the game. For example, a safety ends the game because both teams have had possession of the ball. If one teams kicks a field goal on the opening drive, and then turns around and attempts an onside kick and recovers it, the game is over because both teams have had the opportunity to possess.