Everyone in the group heading off — he wasn't free (5)
I believe the answer is:
helot
'he wasn't free' is the definition.
(helots were slaves in Sparta)
'everyone in the group heading off' is the wordplay.
'everyone in the group' becomes 'the lot' (eg 'the lot of you').
'heading off' means to remove the first letter.
'thelot' with its initial letter taken away is 'HELOT'.
(Other definitions for helot that I've seen before include "Spartan serf" , "Spartan slave" , "One made to work" , "He's bound to land" , "Hotel (anag) - serf" .)