Start to create fuss over ending (4)
I believe the answer is:
coda
'ending' is the definition.
(I have seen 'Musical ending ' mean 'coda' so perhaps 'ending' could also mean 'coda')
'start to create fuss over' is the wordplay.
'start to' indicates taking the first letters.
'fuss' becomes 'ado' ('ado' can be a synonym of 'fuss').
'over' says the letters should be written in reverse.
The initial letter of 'create' is 'c'.
'ado' backwards is 'oda'.
'c'+'oda'='CODA'
(Other definitions for coda that I've seen before include "finish" , "Concluding passage of a musical composition" , "Final part of mus. structure" , "tail" , "Concluding section" .)