Disorder for a month on the border (6)
I believe the answer is:
mayhem
'disorder' is the definition.
(I've seen this before)
'month on the border' is the wordplay.
'month' becomes 'may' (May is an example).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'the border' becomes 'hem' (I've seen this before).
'may'+'hem'='MAYHEM'
'for a' is the link.
(Other definitions for mayhem that I've seen before include "Havoc, violent disturbance" , "Big trouble!" , "Much trouble when" , "Pandemonium" , "Extreme disorder" .)