Having turned back, swimmer out of wind (3)
I believe the answer is:
lee
'out of wind' is the definition.
(as in the lee side, the sheltered side)
'having turned back swimmer' is the wordplay.
'having turned back' shows that the letters should be reversed in order.
'swimmer' becomes 'eel' (eel is a kind of fish).
'eel' in reverse letter order is 'LEE'.
(Other definitions for lee that I've seen before include "Area sheltered from the wind" , "The sheltered side of something" , "Sheltered accommodation" , "The side that's sheltered from the wind" , "Commander of the Confederate States Army in the American Civil War" .)