Possibly scratch hamstring (8)
I believe the answer is:
handicap
This clue could be a double definition.
'possibly scratch' is the first definition.
The definition and answer can be both human attributes as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'hamstring' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for handicap that I've seen before include "Impediment, hindrance" , "It makes progress difficult" , "It impedes or hinders" , "Something making progress or success difficult" , "Grand National for example" .)