Fit in Charlie, playing well (7)
I believe the answer is:
conform
'fit in' is the definition.
(thesaurus)
'charlie playing well' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'playing well' becomes 'on form' (I've seen this before).
'c'+'onform'='CONFORM'
(Other definitions for conform that I've seen before include "Agree" , "Follow the crowd" , "Adapt" , "Match" , "Comply with accepted rules" .)