It's Dean playing as a substitute (7)
I believe the answer is:
instead
'as a substitute' is the definition.
(I've seen this before)
'it's dean playing' is the wordplay.
'playing' indicates an anagram.
'its'+'dean'='itsdean'
'itsdean' anagrammed gives 'INSTEAD'.
(Other definitions for instead that I've seen before include "Alternatively" , "In place (of)" , "As a substitute" , "In lieu" , "as an alternative option" .)