Tense over northern border (2,4)
I believe the answer is:
on edge
'tense' is the definition.
(on edge can mean tense or stressed)
'over northern border' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'border' becomes 'edge' (synonyms).
'o'+'n'+'edge'='ON EDGE'
(Other definitions for on edge that I've seen before include "'Tense, nervous (2,4)'" , "Twitchy" , "Nervy, tense and irritable" , "Tense and irritable, very nervous" , "Apprehensive" .)