Unusually strained exchanges (6,2)
I believe the answer is:
trades in
'exchanges' is the definition.
(trading in is a kind of exchanging)
'unusually strained' is the wordplay.
'unusually' is an anagram indicator.
'strained' anagrammed gives 'TRADES IN'.
(Other definitions for trades in that I've seen before include "Hands over an object as part payment for a new one" , "exchanges" , "'Hands over the old object in part payment for the new (6,2)'" .)