Study good limit (7)
I believe the answer is:
confine
'limit' is the definition.
(I know that limit can be written as confine)
'study good' is the wordplay.
'study' becomes 'con' (con can informally mean to study).
'good' becomes 'fine' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'con'+'fine'='CONFINE'
Can you help me to learn more?
(Other definitions for confine that I've seen before include "Restrict (to an area)" , "Limit" , "pen" , "Shut in" , "Keep within limits" .)