Question: does the puck have to completely cross the line

Answer: Yes, In ice hockey, a goal is scored when the puck entirely crosses the goal line between the two goal posts and below the goal crossbar. A goal awards one point to the team attacking the goal scored upon, regardless of which team the player who actually deflected the puck into the goal belongs to (see also own goal). Typically, a player on the team attempting to score shoots the puck with their stick towards the goal net opening, and a player on the opposing team called a goaltender tries to block the shot to prevent a goal from being scored against their team.