own goal
Synonym discussion
Sense: noun/2
All four describe an action that ends up harming the person who did it. 'Own goal' is a noun borrowed from football, common in British English and journalism, and stresses that you handed the advantage to the other side: 'Closing the only factory was an own goal.' 'Backfire' is a verb and the most neutral choice — any plan can backfire, with no blame implied: 'The surprise party backfired when she found out early.' 'Boomerang' is more vivid and slightly informal, suggesting the harm comes straight back at you: 'His lie boomeranged badly.' 'Self-inflicted wound' is the most dramatic and is favoured in politics, framing the damage as serious and clearly your own fault: 'The leak was a self-inflicted wound for the campaign.'
Etymology
The phrase comes straight from football, where an 'own goal' is a goal a player accidentally puts into the net they are defending, giving the point to the opposing team. By the late twentieth century the term had spread into everyday and political speech for any move that hurts the very side it was meant to help.