own goal

noun2

1. •
   A goal that results from a player putting the ball or puck into the goal of their own team; the resulting goal being scored for the opposition.

   • Madagascar's soccer authorities have banned Stade Olympique de L'Emyrne (SOE)'s coach and four of the team's players after they scored a world record 149 own goals in a match last month. — 2002
2. •
   (figurative) A blunder that damages one’s own prospects.

   • No doubt the buzz of army helicopters will sound again in the skies over Belfast tonight, as loyalists continue to score this series of bloody own goals. — 2011