Missing exercise (8)
I believe the answer is:
skipping
This clue is a double definition.
'missing' is the first definition.
(skipping is a kind of missing)
'exercise' is the second definition.
(skipping is a type of physical exercise)
(Other definitions for skipping that I've seen before include "Jumping lightly or bypassing" , "Jumping with a rope" , "Hopping over a turning rope" , "amusement" , "Playing with a rope" .)