Threw fellow an organ (5)
I believe the answer is:
flung
'threw' is the definition.
(flinging is a kind of throwing)
'fellow an organ' is the wordplay.
'fellow' becomes 'F' (abbreviation - of a society etc.).
'an organ' becomes 'lung' (lung is a kind of organ).
'f'+'lung'='FLUNG'
(Other definitions for flung that I've seen before include "Cast aside" , "Threw" , "Hurled" , "Thrown with force" .)