Athlete’s particularly protective knitted garment? (4,6)
I believe the answer is:
long jumper
'athlete's' is the definition.
(I've seen this before)
'particularly protective knitted garment?' is the wordplay.
'particularly protective' becomes 'long' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'knitted garment?' becomes 'jumper' (I've seen this before).
'long'+'jumper'='LONG JUMPER'
(Other definitions for long jumper that I've seen before include "what covers his or her thighs?" , "one that can touch his knees?" , "Athlete" , "garment that comes down over the thighs?" .)