To play down something means to make it seem less important, serious, or significant than it really is. When a soccer player sprains her ankle but tells the coach “it's nothing,” she's playing down her injury. When a student who studied hard for weeks says “oh, I barely prepared” after acing a test, they're playing down their effort.

People play down things for different reasons. Sometimes they don't want to worry others: a parent might play down concerns about money so their children won't feel anxious. Sometimes they're being modest: an artist might play down praise for her painting by saying “anyone could have done it.” Other times, playing something down can be problematic, like when someone plays down the seriousness of cheating or breaking an important rule.

The phrase suggests a deliberate choice to minimize something. It's the opposite of play up or exaggerate something. A news report might be criticized for playing down the dangers of a storm, or a politician might play down a scandal.