Boy crossing through southern border in a tense state (2,4)
I believe the answer is:
on edge
'tense state' is the definition.
'on edge' can be an answer for 'tense' (on edge can mean tense or stressed). I'm not certain of the 'state' bit.
'boy crossing through southern border in a' is the wordplay.
'boy' becomes 'Ed' (short for Edward).
'crossing through southern border' becomes 'g' (I can't explain this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'a' becomes 'one'.
'ed'+'g'='edg'
'edg' placed into 'one' is 'ON EDGE'.
Can you help me to learn more?
(Other definitions for on edge that I've seen before include "Under stress" , "Highly strung" , "'Tense, nervous (2,4)'" , "Tense and irritable, with nerves stretched" , "stressed" .)