Nutcase takes legal action ending dealings with casual outfits (5,5)

'casual outfits' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'nutcase takes legal action ending dealings' is the wordplay.
'nutcase takes' becomes 'shell' (I can't justify this - if you can you should give a lot more credence to this answer).
'legal action' becomes 'suit' ('suit' can be a synonym of 'legal action').
'ending' says to take the final letters.
The final letter of 'dealings' is 's'.
'shell'+'suit'+'s'='SHELL SUITS'

'with' is the link.

Can you help me to learn more?