To present or perform something in a restrained or subtle manner. The actor chose to underplay his role, giving a more nuanced performance.
To downplay or minimize the importance or significance of something. She tends to underplay her achievements, even though she has accomplished a lot.
In card games, to play a lower card than is required or expected, often to deceive or gain a strategic advantage. She decided to underplay by laying a three of hearts instead of her queen.