Trouble from a guerilla (4)
I believe the answer is:
ague
'trouble' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'a guerilla' is the wordplay.
'guerilla' becomes 'gue' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'gue'='AGUE'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for ague that I've seen before include "Old word for fever" , "Fit of the shakes" , "Malarial fever; chill" , "attack" , "Sickness" .)