play up

Short definition from Wiktionary

Verb

1. 1
   Used other than figuratively or idiomatically: see play, up.
2. 2
   To misbehave.
3. 3
   To make or attempt to make something appear more important, likely, or obvious; to showcase or highlight.
4. 4
   To play (e.g. sport or music) more vigorously.
5. 5
   To be unfaithful to a lover; to cheat; used with on.