Jockey stymied if thrown (9)
I believe the answer is:
mystified
'thrown' is the definition.
('mystify' can be a synonym of 'throw')
'jockey stymied if' is the wordplay.
'jockey' indicates an anagram (I've seen this in other clues).
'stymied'+'if'='stymiedif'
'stymiedif' with letters rearranged gives 'MYSTIFIED'.
(Other definitions for mystified that I've seen before include "Puzzled, really baffled" , "confused" , "Perplexed" , "Seriously puzzled" , "Utterly bewildered" .)