Pain during doggy paddle (3)
I believe the answer is:
gyp
'pain' is the definition.
(I've seen this before)
'during doggy paddle' is the wordplay.
'during' indicates a hidden word.
'GYP' is hidden within 'doggy paddle'.
(Other definitions for gyp that I've seen before include "Swindle - pain - college servant" , "Cheat - discomfort" , "college employee" , "Torture (sl.)" , "Pain (slang)" .)