Jaunty one bitten by shark at sea (6)
I believe the answer is:
rakish
'jaunty' is the definition.
('rakish' can be a synonym of 'jaunty')
'one bitten by shark at sea' is the wordplay.
'one' becomes 'i' (Roman numeral).
'bitten by' is an insertion indicator (I've seen this in other clues).
'at sea' indicates an anagram.
'shark' with letters rearranged gives 'raksh'.
'i' placed inside 'raksh' is 'RAKISH'.
(Other definitions for rakish that I've seen before include "Marked by unconventionality or disreputableness" , "Given to philandering" , "Dashing, devil-may-care" , "Jaunty; dissolute" , "Jaunty; fast-looking (boat)" .)