Frenzied sailor free to go round (5)
I believe the answer is:
rabid
'frenzied' is the definition.
(I've seen this before)
'sailor free to go round' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'free' becomes 'rid' (to be free of something is to be rid of it).
'to go round' means one lot of letters goes inside another.
'ab' inserted inside 'rid' is 'RABID'.
(Other definitions for rabid that I've seen before include "Ferocious" , "Extremely fanatical" , "Burning" , "Frenzied" , "extremist" .)