It's silly to crave ham (7)
I believe the answer is:
overact
'ham' is the definition.
('overact' can be a synonym of 'ham')
'it's silly to crave' is the wordplay.
'it's silly' indicates an anagram.
'to'+'crave'='tocrave'
'tocrave' is an anagram of 'OVERACT'.
(Other definitions for overact that I've seen before include "pile it on" , "behave exaggeratedly" , "Do what ham thespian does" , "Exaggerate" , "Play part exaggeratedly" .)