Racecourse for one north of the border (5)
I believe the answer is:
ascot
'racecourse' is the definition.
(British racecourse)
'for one north of the border' is the wordplay.
'for one' becomes 'csa' (I can't explain this - if you can you should give a lot more credence to this answer).
'north' says the letters should be written backwards (in a down clue, letters go up or 'northward').
'border' indicates taking the first letters.
The first letters of 'of the' is 'ot'.
'csa' backwards is 'asc'.
'asc'+'ot'='ASCOT'
Can you help me to learn more?
(Other definitions for ascot that I've seen before include "Famous racecourse" , "Tosca (anag) - racecourse" , "track" , "sporting event" , "sporting venue" .)