Sportsperson held hostage by eleven terrorists (7)
I believe the answer is:
eventer
'sportsperson' is the definition.
'held hostage by eleven terrorists' is the wordplay.
'held hostage by' indicates the answer is hidden within the clue.
'EVENTER' is hidden within 'eleven terrorists'.
(Other definitions for eventer that I've seen before include "Equestrian competitor" , "Equestrian horse" , "competitive horse" , "versatile horse" , "Competitive horse/rider" .)