Vie in tussle with agent? No (8)
I believe the answer is:
negative
'no' is the definition.
(I've seen this before)
'vie in tussle with agent?' is the wordplay.
I cannot really see how this works, but
an anagram of 'vie' is 'ive' which is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for negative that I've seen before include "Pessimistic, discouraging" , "Less than zero, minus" , "Gloom-ridden" , "Photographic image with tones reversed" , "Film with images reversed" .)