Competed in medieval combat re-enactment topless, getting thrown out! (6)
I believe the answer is:
ousted
'thrown out' is the definition.
('oust' can be a synonym of 'throw out')
'competed in medieval combat re-enactment topless' is the wordplay.
'competed in medieval combat re-enactment' becomes 'jousted' (jousting was a medieval sport).
'topless' means to remove the first letter.
'jousted' with its initial letter removed is 'OUSTED'.
'getting' acts as a link.
(Other definitions for ousted that I've seen before include "Offences against the law of the land" , "Booted out of office" , "Put out of office by force" , "Ejected or expelled" , "Drove or ejected from office" .)