Workout garments - father wearing set wasn't relaxed (10)
I believe the answer is:
'workout garments' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'father wearing set wasn't relaxed' is the wordplay.
'father' becomes 'pa' (pa is a kind of father).
'wearing' indicates putting letters inside.
'relaxed' is an anagram indicator.
'setwasnt' with letters rearranged gives 'sweatnts'.
'pa' put inside 'sweatnts' is 'SWEATPANTS'.
Can you help me to learn more?
(Other definitions for sweatpants that I've seen before include "clothing" , "Loose, warm garment - wasn't a pest (anag)" , "Sports bags" , "Joggers" .)