The duration of a hockey game in the National Hockey League (NHL) or any other professional hockey leagues is 60 minutes which is divided into 3 halves. Each half consists of 20 minutes. Unlike football, the timer is stopped whenever there is an interruption in the game. At the end, if the game results into a draw, it is likely to have an overtime to decide the winner.
The overtime is composed of five minutes and it only takes place if the game is drawn during the normal time. In this crucial phase, instead of having five skaters there are only four skaters on the ice. As the number of skaters on the ice decreases, the opportunity to score a goal immediately increases. As soon as the puck crosses the goal line, the game ends. The team which scores first in this overtime is announced as the winner of the match. And that is why, perhaps, it is called “sudden death” overtime.