Treated badly with forces leaving, crowd united (3-4)
I believe the answer is:
ill-used
'treated' is the definition.
(ill-using is a kind of treating)
'badly with forces leaving crowd united' is the wordplay.
'badly' becomes 'ill' ('ill' can be adverbial as in 'ill-advised').
'with' says to put letters next to each other.
'forces leaving' becomes 'use' (I can't explain this - if you can you should give a lot more credence to this answer).
'crowd' becomes 'd'.
'united' means one lot of letters go next to another.
'ill'+'use'+'d'='ILL-USED'
Can you help me to learn more?
(Other definitions for ill-used that I've seen before include "Badly treated, exploited" , "Mistreated" , "Maltreated" .)