Play fringe - it's where the profit is (6)
I believe the answer is:
margin
'play' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for margin that I've seen before include "Boundary line or the area" , "bank" , "Permissible difference" , "Blank space around the edge" , "Edge; room for error" .)