Man upset nowadays by North (3)
I believe the answer is:
dan
'man' is the definition.
'upset nowadays by north' is the wordplay.
'upset' shows that the letters should be reversed in order.
'nowadays' becomes 'ad'.
'by' says to put letters next to each other.
'north' becomes 'n' ('N' can be a synonym of 'north').
'ad' back-to-front is 'da'.
'da'+'n'='DAN'
(Other definitions for dan that I've seen before include "Level of proficiency in Japanese combative sport" , "Grade of judo black belt" , "Dark and damp." , "Proficient combative sportsman" , "degree of proficiency in judo, say?" .)