Create case for trade after classes (8)
I believe the answer is:
generate
'create' is the definition.
(generating is a kind of creating)
'case for trade after classes' is the wordplay.
'case for' means to remove the middle letters (the letters which encase the others are used).
'after' says to put letters next to each other.
'classes' becomes 'genera' (more than one genus - a class or category).
'trade' with its middle taken out is 'te'.
'te' after 'genera' is 'GENERATE'.
(Other definitions for generate that I've seen before include "Engender" , "Bring into existence for teenager" , "Produce, create" , "Produce - teenager (anag)" , "Beget" .)