Nut by net's opposite rivet (7)
I believe the answer is:
engross
'rivet' is the definition.
(I know that rivet is a more specific form of engross)
'nut by net's opposite' is the wordplay.
'nut' becomes 'en' ('nut' is printers' slang for an en space).
'by net's opposite' becomes 'gross' (I can't explain this - if you can you should believe this answer much more).
'en'+'gross'='ENGROSS'
Can you help me to learn more?
(Other definitions for engross that I've seen before include "Totally absorb the attention of" , "Rivet" , "Occupy attention fully, absorb" , "Absorb the attention of (someone)" , "grab attention" .)