Anger about northern army practice area (5)
I believe the answer is:
range
'army practice area' is the definition.
(as in a military range)
'anger about northern' is the wordplay.
'anger' becomes 'rage' (rage is a kind of anger).
'about' is an insertion indicator.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'rage' enclosing 'n' is 'RANGE'.
(Other definitions for range that I've seen before include "Open grazing land or cooking stove" , "Compass - scope" , "specific category" , "Full choice of clothes" , "Stove; variety" .)