own goal 
noun
1(In soccer) a goal scored when a player inadvertently strikes or deflects the ball into their own team’s goal.To add insult to injury the final goal was an own goal by the Abbey centre half....
- Who has scored the most own goals in English football history?
- A team may win a game 5-1, but it can still score an own goal, have three yellow cards and a player sent off.
1.1British informal An act that unintentionally harms one’s own interests: government scores own goal by assisting organized crime in London...
- A political party cannot afford to score own goals like these so close to an election.
- What's more, in trying to compete in the ever-changing world of broadcasting, the BBC has scored an own goal.
- The Conservative MP scored an embarrassing own goal yesterday as he tried to put a string of damaging headlines behind him.