Roams ruin, upsetting some stars (4,5)
I believe the answer is:
ursa minor
'some stars' is the definition.
(I've seen this before)
'roams ruin upsetting' is the wordplay.
'upsetting' indicates an anagram.
'roams'+'ruin'='roamsruin'
'roamsruin' with letters rearranged gives 'URSA MINOR'.
(Other definitions for ursa minor that I've seen before include "Paddington, say" , "Group appearing nightly" , "Paddington, for example" , "Group of stars" , "Little Bear constellation, to the old Romans" .)