This is another rule put into place to keep the flow of a hockey game smooth with a minimal amount of whistles.  The more whistles a hockey game has, the more choppy the play gets, and the more penalties have to be called because the players start to play a choppy, clutch and grab style of hockey.

A goaltender who plays the puck is not allowed to shoot the puck directly out of the playing surface in order to get a whistle.  You are likely to see a goaltender do such an action when his team is having trouble getting the puck out of their end or they need a whistle because they are getting tired.  Most of the time this happens by accident when the goalie is trying to get the puck out of his end zone. If goalies were allowed to shoot the puck out of the playing surface then there would be more whistles throughout a game and thus you would see a choppier style of play.

When a goalie shoots the puck towards the boards, the referee must now watch what happens to the puck.  If the puck goes above the glass then a penalty will be assessed only if the puck went over the height of the tallest portion of glass. 

For instance, in most arenas the glass is designed higher behind the nets and it usually extends around the corners of the ice surface to about the hash marks.  Then the glass usually drops a few feet in height from one end zone hash marks to the other end zone hash marks on one side of the ice.  On the other side of the ice (arenas with benches on same side of the ice) the benches do not have glass in front of them because this would limit players from being able to change quicker by not allowing them to jump over the boards.

If a goalie shoots the puck over the glass and in the opinion of the referee the puck went over the glass, but not over the highest portion of glass (between the lowest portion of glass and tallest portion of glass), then no delay of game penalty has to be assessed. This is just like the goalie shooting the puck over the portion of the players’ bench.  Since there is no glass in this area a delay of game penalty is not assessed, unless the goalie shoots the puck at a height that would have in the opinion of the referee, gone over the tallest portion of glass (height of glass behind net). In order to enforce this rule the referee must picture the height of the glass behind the net extending around the entire ice surface.

This last point is a very important one. Many coaches and players, as well as parents and fans, think that a goalie can only be penalized if he shoots the puck over the glass in his end zone.  However, if he is strong enough to lift the puck half way down the rink and it goes over the player’s bench, he can still be given a penalty as long as it goes high enough to have been able to clear the highest point of the glass around the end boards.

If the goalie shoots the puck and it hits the glass, a player, or official before going  over the tallest portion of glass, then there will be no penalty assessed to the goalie because the puck did not go ‘directly’ out of the playing zone. If it hits an object or a person first, it is considered to have been deflected over the glass