Reduce study, being stupid (8)
I believe the answer is:
condense
'reduce' is the definition.
(condensing is a kind of reducing)
'study being stupid' is the wordplay.
'study' becomes 'con' (I've seen this before).
'being stupid' becomes 'dense' ('dense' can be similar in meaning to 'stupid').
'con'+'dense'='CONDENSE'
(Other definitions for condense that I've seen before include "Send once (anag.)" , "Make more concise" , "Abridge" , "Abbreviate" , "precis" .)