Stickler for niceties hurt in physical training (13)
I believe the answer is:
perfectionist
'stickler' is the definition.
(I have seen 'The Stickler' mean 'perfectionist' so perhaps 'stickler' could also mean 'perfectionist')
'for niceties hurt in physical training' is the wordplay.
'hurt' is an anagram indicator.
'in' means one lot of letters goes inside another.
'physical training' becomes 'pt'.
'for'+'niceties'='forniceties'
'forniceties' with letters rearranged gives 'erfectionis'.
'erfectionis' put into 'pt' is 'PERFECTIONIST'.
(Other definitions for perfectionist that I've seen before include "One striving for an ideal standard" , "I expect the best" , "Striver for the ideal" , "One seeking the ideal" , "The Stickler" .)