The objective of hockey is simple: score more goals than the opposing team. Players are not allowed to kick the puck into the net or purposely direct it in with any part of their body. During regulation time, each team uses five skaters—three forwards and two defencemen—plus a goaltender. National Hockey League games are contested over three 20-minute periods. If the score is tied after 60 minutes, the game moves to a five-minute, sudden-death overtime where the first goal wins. If the game remains tied after overtime, a shootout is held until a winner is determined. There are four officials in NHL games—two referees and two linesmen. They stop play for penalties and for things like offside or icing. Offside: when players enter the offensive zone before the puck gets there.