does the english translation make sense? i'm not a sport fanatic, so what's an "own goal"?
It means the player scored in the goal they're trying to defend, rather than the opponent's goal. It usually happens by mistake, for example, if a defender tries to block a shot that was initially going wide anyway, but ends up redirecting it into the goal.
It is an own goal (OG), you can ask the poor northern Irelender, MaCauley who scored one yesterday and so his team is out of the Euro now :P
Sounds weird to me too, what do you call it when a player scores for the other team by mistake? That is the meaning of שער עצמי. It is also used metaphorically sometimes, to express acting against one's own interests. It's not exactly an expression, but a common metaphor.
In North America, we tend more to say "he scored on himself" or something similar. The phase "an own goal" isn't well known.