1. In cricket, to score one's first run of an inning, especially after a string of innings during which one has failed to score (one of which is known as a duck). Primarily heard in UK. Their esteemed batsman, having an unusually poor performance today, finally broke his duck midway through the match.

2. In sports, to score or accomplish something for the first time. Refers to cricket, where it means to score one's first run of an inning. Primarily heard in UK. The team's star striker broke her duck just minutes into the game.