Fellow to steer away? Rot (6)
I believe the answer is:
fester
'rot' is the definition.
(I've seen this in another clue)
'fellow to steer away?' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'to' means one lot of letters go next to another.
'away?' is an anagram indicator (letters move away from their original places).
'steer' anagrammed gives 'ester'.
'f'+'ester'='FESTER'
(Other definitions for fester that I've seen before include "Rankle" , "Go septic or cause resentment" , "Ripen and generate pus" , "Become rotten, bitter or irritated" , "strange uncle" .)