People injured by throwaway garments? (10)

I believe the answer is:

casualties

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'people injured' is the definition.
I know that 'injured' relates to this answer.

'throwaway garments?' is the wordplay.
'throwaway' becomes 'casual' (I am not sure about this - if you are sure you should believe this answer much more).
'garments?' becomes 'ties' (tie is a kind of garment).
'casual'+'ties'='CASUALTIES'

'by' is the link.

Can you help me to learn more?

(Other definitions for casualties that I've seen before include "Injured people" , "Victims" .)

I've seen this clue in The Guardian.

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