Run off report by one of those associated with The Plague (4)
I believe the answer is:
flea
'one of those associated with the plague' is the definition.
I can't tell whether this definition defines the answer.
'run off report' is the wordplay.
'run off' becomes 'flee' (I've seen this before).
'report' indicates a 'sounds like' (homophone) clue.
'flee' is a homophone of 'FLEA'.
'by' is the link.
Can you help me to learn more?
(Other definitions for flea that I've seen before include "Bug" , "Insect (which you don't want in your ear!)" , "In one's ear, it's a stinging rebuke" , "high-jumper" , "little pest" .)