Rare hound, ten, on right, collapsing (4,2,3,6)
I believe the answer is:
thin on the ground
'rare' is the definition.
(I've seen this before)
'hound ten on right collapsing' is the wordplay.
'collapsing' indicates anagramming the letters.
'hound'+'ten'+'on'+'right'='houndtenonright'
'houndtenonright' anagrammed gives 'THIN ON THE GROUND'.
(Other definitions for thin on the ground that I've seen before include "description of weedy fighter after KO?" , "Present in very small numbers" , "scarce" , "Rare" , "A sprinkling of snow" .)