Go to excess because of function? (6)
I believe the answer is:
overdo
'go to excess' is the definition.
(I've seen this in another clue)
'because of function?' is the wordplay.
'because of' becomes 'over' (eg 'he's upset over it').
'function?' becomes 'do' (both can mean an event).
'over'+'do'='OVERDO'
(Other definitions for overdo that I've seen before include "Cook too long or act excessively" , "Sum of a persons actions (Hinduism)" , "Carry too far" , "Take too far" , "Put too much effort into" .)