Caught swimmer, one with a good ear? (5)
I believe the answer is:
tuner
'one with a good ear?' is the definition.
(person who tunes musical instruments)
'caught swimmer' is the wordplay.
'caught' indicates a 'sounds like' (homophone) clue (to catch something can mean to hear it).
'swimmer' becomes 'tuna' (tuna is a type of fish).
'tuna' is a homophone of 'TUNER'.
(Other definitions for tuner that I've seen before include "Piano adjuster" , "Radio receiver" , "Adjuster of pianos" , "Radio adjuster" , "Motor specialist" .)