losing accidentally; defeat due to a mistake
Used in competitive contexts when a loss is caused by one's own error or bad luck rather than the opponent's superior skill. Often seen in sports or games.
That match was a complete accidental loss.
I lost accidentally because of a careless mistake.
Compound of 怪我 (けが, 'injury; accident') and 負け (まけ, 'defeat'). The exact historical derivation is uncertain, but the word transparently means 'losing due to an accident or mistake'.