Cat catching beam displays assertive behaviour (9)
I believe the answer is:
pushiness
'assertive behaviour' is the 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?
'cat catching beam' is the wordplay.
'cat' becomes 'puss' (puss is a kind of cat).
'catching' is an insertion indicator.
'beam' becomes 'shine' (synonyms).
'puss' going around 'shine' is 'PUSHINESS'.
'displays' is the link.
Can you help me to learn more?
(Other definitions for pushiness that I've seen before include "Ambitious quality" , "Self-assertion; ambition" .)