In American football, a field goal is worth three points. In order to receive credit for a field goal, the kicker for the offensive line has to successfully kick the ball through the goal posts on the defensive team's end zone.
Scoring points through this method is preventable just like a touch-down or any other form of scoring. Icing the kicker is the most common method that is used to prohibit the scoring of the field goal. This is where a time-out is called by the defense in an attempt to interrupt the goal kicker's preparation to make the play.