Especially on a training session, we hear casual shoe (10)
I believe the answer is:
espadrille
'casual shoe' is the definition.
(type of shoe)
'especially on a training session we hear' is the wordplay.
'especially' becomes 'esp' (common abbreviation).
'on' says to put letters next to each other.
'training session' becomes 'drill' (eg a military drill).
'we hear' shows a homophone (sound like).
'drill' is a homophone of 'drille'.
'esp'+'a'+'drille'='ESPADRILLE'
(Other definitions for espadrille that I've seen before include "sandal!" , "[SHOE], made casually" , "you put your foot in it" , "Light rope-soled shoe" , "Shoe with a canvas upper" .)