Applaud a pupil for coming in top (4)
I believe the answer is:
clap
'applaud' is the definition.
(synonyms)
'a pupil for coming in top' is the wordplay.
'a pupil for' becomes 'l' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'coming in' means one lot of letters goes inside another.
'top' becomes 'cap' (cap is a kind of top).
'l' placed into 'cap' is 'CLAP'.
Can you help me to learn more?
(Other definitions for clap that I've seen before include "express approval" , "Sudden loud noise (of thunder?)" , "Audibly show approval" , "Make sound of applause" , "Applaud manually" .)