Like jerks, heartless grey men lead in this sport (10)
I believe the answer is:
gymnastics
'this sport' is the definition.
(gymnastics is a kind of sport)
'like jerks heartless grey men lead' is the wordplay.
I cannot really see how this works, but
'like' could be 'y' (similar in meaning) and 'y' is located in the answer.
'jerks' could be 'tics' and 'tics' is found in the answer.
This explanation may well be incorrect...
'in' acts as a link.
(Other definitions for gymnastics that I've seen before include "Athletic exercises" , "Sporting exercise" , "Callisthenics" , "Acrobatic exercises" , "Acrobatics" .)