Caught, not many would quarrel at length (4)
I believe the answer is:
feud
'quarrel at length' is the definition.
'caught not many would' is the wordplay.
I cannot quite understand how this works, but
'many' could be 'd' (Roman numeral for 500) and 'd' is present in the answer.
The remaining letters 'feu' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for feud that I've seen before include "Sustained enmity" , "Private war" , "quarrel without end" , "Long-running disagreement" , "Vendetta" .)