Drunkard swims badly in a coma (11)
I believe the answer is:
dipsomaniac
'drunkard' is the definition.
(dipsomaniac is a kind of drunkard)
'swims badly in a coma' is the wordplay.
'swims' becomes 'dips' (dip is a kind of swim).
'badly' indicates anagramming the letters.
'in'+'a'+'coma'='inacoma'
'inacoma' anagrammed gives 'omaniac'.
'dips'+'omaniac'='DIPSOMANIAC'
(Other definitions for dipsomaniac that I've seen before include "Hard drinker" , "drunkard" , "Alcoholic" , "wino" , "Habitual drinker" .)