Swimmer out of breath? (6)
I believe the answer is:
bather
'swimmer' is the definition.
(I know that swimmer can be written as bather)
'of breath?' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'breath' anagrammed gives 'BATHER'.
'out' acts as a link.
(Other definitions for bather that I've seen before include "Seaside swimmer" , "one getting into the drink" , "One dipping in the briny?" , "man getting soaked?" .)