own goal

noun
  1. soccer a goal scored by a player accidentally playing the ball into his own team's netAbbreviation: o.g
  2. informal any action that results in disadvantage to the person who took it or to a party, group, etc with which that person is associated
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012