Fight interrupts fine sporting action (5,2)
I believe the answer is:
throw in
'sporting action' is the definition.
(I've seen this before)
'fight interrupts fine' is the wordplay.
'fight' becomes 'row' (I've seen this in another clue).
'interrupts' is an insertion indicator.
'fine' becomes 'thin' (similar in meaning).
'row' going into 'thin' is 'THROW-IN'.
(Other definitions for throw in that I've seen before include "play in football match" , "restart for game" , "feature of football" , "chance to get back into the game" , "Manual delivery" .)