Perform some forbidden activities (5)
I believe the answer is:
enact
'perform' is the definition.
(I've seen this before)
'some forbidden activities' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ENACT' is hidden within 'forbidden activities'.
(Other definitions for enact that I've seen before include "Present" , "Pass into law" , "Put on stage or statute book" , "Authorize" , "Official order" .)