To misbehave.
Children who do not receive enough attention may begin to play up.
To make or attempt to make something appear more important, likely or obvious; to showcase or highlight.
For the audition, Nicole will play up her skill as a pianist by playing Jesu, Joy of Man's Desiring by Bach.
To play more vigorously.
To be unfaithful to a lover; to cheat; used with on.