Surprisingly cast net, not being a competitor (10)
I believe the answer is:
contestant
'a competitor' is the definition.
(thesaurus)
'surprisingly cast net not' is the wordplay.
'surprisingly' indicates an anagram.
'cast'+'net'+'not'='castnetnot'
'castnetnot' anagrammed gives 'CONTESTANT'.
'being' is the link.
(Other definitions for contestant that I've seen before include "Person vying with others" , "Candidate" , "Competitor" , "One entering a competition" , "Player" .)