Backside converted poor tries (9)
I believe the answer is:
posterior
'backside' is the definition.
(I know that backside can be written as posterior)
'converted poor tries' is the wordplay.
'converted' indicates an anagram.
'poor'+'tries'='poortries'
'poortries' anagrammed gives 'POSTERIOR'.
(Other definitions for posterior that I've seen before include "Behind" , "later" , "Rear" , "Backside" , "Further back; bottom" .)