The goal a team is guarding.
When a player accidentally kicks, heads or knocks the ball into his own goal. The point is awarded to the offensive team.
A player accidentally putting the ball in his own net, thus scoring a goal for the opposing team.
When a defender accidently scores in his goal.
A goal scored by a player into his own team's net. If a shot is taken and the ball deflects off a defender for a goal, the goal is considered to have been scored by the player taking the shot, and is not an own goal.
An own goal occurs in goal-scoring games when a player scores a goal that is registered against his own team. It is usually accidental, and may be a result of an attempt at defensive play that failed or was spoiled by opponents.