Layabout upset by occasionally chaotic dancers (7)
I believe the answer is:
bolshoi
'dancers' is the definition.
(Bolshoi Ballet in Russia)
'layabout upset by occasionally chaotic' is the wordplay.
'layabout' becomes 'slob' (both can mean a lazy person).
'upset' is a reversal indicator.
'by' means one lot of letters go next to another.
'occasionally' means one should take alternating letters.
The alternate letters of 'chaotic' are 'hoi'.
'slob' backwards is 'bols'.
'bols'+'hoi'='BOLSHOI'
(Other definitions for bolshoi that I've seen before include "Great Moscow ballet company" , "Moscow's ballet" , "Famous Moscow ballet company" , "Moscow theatre (ballet, etc)" , "Russian ballet company" .)