NFL New Overtime Rule
Both teams must have the opportunity to possess the ball once during the extra period, unless the team that receives the opening kickoff scores a touchdown on its initial possession, in which case it is the winner.
If the team that possesses the ball first scores a field goal on its initial possession, the other team shall have the opportunity to possess the ball. If that team scores a touchdown on its possession, it is the winner. If the score is tied after both teams have a possession, the team next scoring by any method shall be the winner.
If the score is tied at the end of a 15-minute overtime period, or if the overtime period's] initial possession has not ended, another overtime period will begin, and play will continue until a score is made, regardless of how many 15-minute periods are necessary.