Influence of fellows, English, in performance (6)
I believe the answer is:
affect
'influence' is the definition.
(I know that influence is a more specific form of affect)
'fellows english in performance' is the wordplay.
'fellows' becomes 'ff' (an abbreviation for fellow written twice).
'english' becomes 'E' (abbreviation).
'in' means one lot of letters goes inside another.
'performance' becomes 'act' (act is a kind of performance).
'ff'+'e'='ffe'
'ffe' placed into 'act' is 'AFFECT'.
'of' acts as a link.
(Other definitions for affect that I've seen before include "impress" , "Have repercussions on" , "Pretend to feel or arouse sadness" , "front" , "Arouse sadness or sympathy like tear-jerker" .)