Step demonstrated by fan in the middle of exercise (4)
I believe the answer is:
pace
'step' is the definition.
(I know that pace is a type of step)
'fan in the middle of exercise' is the wordplay.
'fan in' becomes 'pac' (I can't justify this - if you can you should give a lot more credence to this answer).
'the middle of' says to take the centre.
'exercise' becomes 'leg exercise' (leg exercise is a kind of exercise).
The middle letter of 'leg' is 'e'.
'pac'+'e'='PACE'
'demonstrated by' is the link.
Can you help me to learn more?
(Other definitions for pace that I've seen before include "Part of step" , "Tempo, rate of moving" , "With due respect" , "politely expressing disagreement" , "Clip" .)