Go off fellow and steer away (6)
I believe the answer is:
fester
'go off' is the definition.
(I've seen this before)
'fellow and steer away' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'and' says to put letters next to each other.
'away' indicates anagramming the letters (letters move away from their original places).
'steer' is an anagram of 'ester'.
'f'+'ester'='FESTER'
(Other definitions for fester that I've seen before include "Suppurate" , "Rot" , "Of wound, form yellow pus" , "Go septic or cause resentment" , "Ripen and generate pus" .)