Observe cutting going up and down (9)
I believe the answer is:
seesawing
'going up and down' is the definition.
(I've seen this before)
'observe cutting' is the wordplay.
'observe' becomes 'see' (observe can mean to see something).
'cutting' becomes 'sawing' (sawing is a kind of cutting).
'see'+'sawing'='SEESAWING'
(Other definitions for seesawing that I've seen before include "Swinging" , "going up and down" , "may show fluctuation" .)