Ice hockey is played on a rectangular rink with curved corners whose length may vary from 184 to 200 ft (56–61 m), its width from 85 to 98 ft (26–30 m). Six players—a goalie, a center, two defensemen, and two forwards—all of whom are on ice skates, make up a team. The rink is surrounded on all sides by walls 31/2 to 4 ft (1.06–1.22 m) high. The goal mouths are 4 ft (1.22 m) high and 6 ft (1.83 m) wide and are set 10 ft (3.05 m) out from each end of the rink, which is divided by colored lines in the ice into three zones (attacking, neutral, and defending) that are each 60 ft (18.29 m) long. A puck, once made of rubber but now of composite material, 1 in. (2.54 cm) thick and 3 in. (7.62 cm) in diameter, and frozen to reduce resiliency, is the object used in play. The weight, size, and shape of the sticks used to hit the puck are standardized. After a face-off (the dropping of the puck between two opposing players by an official), the team in possession of the puck seeks to maneuver it past the other team and into its net. Each goal counts one point. The game is divided into three 20-min periods; overtime periods in case of ties are used in certain professional games. In this fast and body-bruising sport, players use heavy protective equipment, and there is unlimited substitution. A player detected by the referee in roughing, tripping, high-sticking, or other violations must spend two minutes (a minor penalty) or more (major penalties) off the ice in the penalty box, and his team must continue play shorthanded. Linesmen, goal judges, a timekeeper, and a scorer also officiate.