In order to play there are X number of players and a specifically appointed goalkeeper. This is a two part question. If the goalkeeper is injured does play stop? If the keeper is injured for a period of time and play is continuing does the goal count if it crosses the goal line?
USSF answer (July 29, 2010):
A two-part question gets a two-part answer.
1. Play is stopped only if, in the opinion of the referee, the player is seriously injured. That includes all players, whether field player or goalkeeper.
2. If the goalkeeper is not, in the opinion of the referee, seriously injured and play continues, a goal would be counted if the whole of the ball completely crosses the entire goal line between the goalposts and beneath the crossbar.