To sandbag means to hide your true abilities or strength so others underestimate you, giving you an advantage later. In a spelling bee, a student who pretends to struggle with easy words but then breezes through the championship round is sandbagging. In sports, a team that plays lazily during practice but dominates in the actual game might be accused of sandbagging.

Today, people sandbag in all kinds of situations: a chess player might sandbag their ranking to face easier opponents, or a business might sandbag its sales forecast so it looks impressive when it exceeds it.

Sandbagging is generally considered sneaky and unfair because it involves deliberate deception. It's different from simply doing your best when it counts. Someone who studies hard for a test isn't sandbagging, but someone who acts like they didn't study at all (when they actually did) to make others feel overconfident is definitely sandbagging.

The word can also mean to criticize or treat someone harshly, though this meaning is less common. You might hear someone say, “Don't sandbag me for one mistake.”