own goal

own goal (plural own goals)

1. (sports) A goal that results from a player putting the ball or puck into the goal of his or her own team; the resulting goal being scored for the opposition.
   • 2014, Jeremy Wilson, “Andrés Escobar murder: Colombia prepare for biggest ever World Cup match on 20th anniversary of death,” The Daily Telegraph, 2 July, 2014,

     It is 20 years to the day since Escobar was shot dead after scoring the own goal that effectively sealed Colombia’s elimination from USA ’94.

2. (figuratively) A blunder that damages one’s own prospects.
   • 2011, Fionola Meredith, “Belfast riots are an own goal,” The Guardian, 22 June, 2011,

     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.

   • 2017, Sotirios Zartaloudis, “Theresa May wins election, but ends up the biggest loser,” The Globe and Mail, 9 June, 2017,

     These elections mark a personal humiliation for incumbent Ms. May, who ran a very personalized campaign as a “strong and stable” leader asking British voters to give her a clear mandate to negotiate Brexit. Ms. May scored an unforced own goal by reducing her party’s parliamentary seats and absolute majority.

• dig one's own grave
• self-inflicted
• shoot oneself in the foot