Showing flexibility, not starting and stopping (6)
I believe the answer is:
ending
'stopping' is the definition.
('end' can be a synonym of 'stop')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for ending that I've seen before include "terminal" , "Finishing" , "Gin den (anag.)" , "Finale" , "Coda" .)