Upsetting kind of trap used by a large town, demonstrates their determination (8)
I believe the answer is:
tenacity
'determination' is the definition.
(tenacity is a kind of determination)
'upsetting kind of trap used by a large town' is the wordplay.
'upsetting' shows that the letters should be reversed in order.
'kind of trap' becomes 'net'.
'used by' is a charade indicator (letters next to each other).
'large town' becomes 'city' (a city is a large settlement).
'net' written backwards gives 'ten'.
'ten'+'a'+'city'='TENACITY'
'demonstrates their' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tenacity that I've seen before include "Perseverance, doggedness" , "Persistent determination, doggedness" , "Doggedly pursuing" , "Bulldog quality" , "Firmness of hold" .)