winning accidentally; winning by default due to opponent's injury
Used in competitive contexts (sports, games) when a victory is obtained because the opponent is injured or unable to continue, rather than through superior skill. Often carries a nuance of an undeserved or lucky win.
I won by default because my opponent withdrew due to injury.
The final match ended in an accidental win due to injury, and I have mixed feelings.
勝利 is a general term for victory, without the nuance of luck or opponent's misfortune. 怪我勝ち emphasizes the accidental nature of the win.
Compound of 怪我 (けが, injury) and 勝ち (がち, winning). The reading がち is a rendaku form of 勝ち (かち).