<P> The rules differ slightly from the rules used in international games organized by the International Ice Hockey Federation (IIHF) such as the Olympics (the NHL rules, however, are used in the World Cup of Hockey). The IIHF rules are themselves also based on Canadian rules of ice hockey dating back to the early 20th Century . The NHL and IIHF differ in the treatment of fighting and in playing rules, such as icing, the areas of play for goaltenders, helmet rules, officiating rules, timeouts and play reviews . </P> <P> Near each end of the rink there is a red goal line spanning the width of the ice . It is used to judge goals and icing calls . </P> <P> New since the 2005--06 NHL season, after testing in the American Hockey League, a trapezoid is marked behind each goalie net . The goalie can only play the puck within that area or in front of the goal line . If he plays the puck behind the goal line and not in the trapezoid, a 2 - minute minor penalty for delay of game will be assessed by the referees . This rule is widely referred to as the "Brodeur rule", after New Jersey Devils goalie Martin Brodeur, whose puckhandling behind the net is believed to be the cause for the rule . In 2014, the NHL lengthened the goal - line side of the trapezoid by two feet on both sides of the net . </P> <P> In the National Hockey League, between stoppages of play, teams have 18 seconds (five seconds for the visiting team, eight seconds for the home team, five seconds to line up at the faceoff location) to substitute their players, except during TV timeouts . TV timeouts are two minutes long, and occur three times per period, during normal game stoppages after the 6, 10, and 14 minute marks of the period, unless there is a power play, a goal that has just been scored, or the stoppage was as a result of an icing . Each team may also take one 30 second time - out, but it may only be taken during a normal stoppage of play . Each period, teams rotate nets, therefore changing attacking directions . </P>

What is the purpose of the trapezoid in hockey
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