Exercise set: one’s somersaulting (3-2)
I believe the answer is:
sit-up
'exercise' is the definition.
(I've seen this before)
'set one's somersaulting' is the wordplay.
I cannot quite see how this works, but
'set' could be 'sit' (sitting is a kind of setting) and 'sit' is found within the answer.
The remaining letters 'up' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sit-up that I've seen before include "Exercise done on the floor" , "Exercise designed to strengthen stomach muscles" , "Physical exercise" .)