Informal empty trolley for one who's injured (8)
I believe the answer is:
casualty
'one who's injured' is the definition.
I know that 'injured' relates to this answer.
'informal empty trolley' is the wordplay.
'informal' becomes 'casual' (similar in meaning).
'empty' says to hollow out the word (remove centre letters).
'trolley' with its middle removed is 'ty'.
'casual'+'ty'='CASUALTY'
'for' is the link.
Can you help me to learn more?
(Other definitions for casualty that I've seen before include "TV hospital drama" , "Victim of accident or war" , "Distance across circle" , "Person injured or killed" , "Wounded victim" .)