Rush to the north side before crossing east (5)
I believe the answer is:
haste
'rush' is the definition.
(I know that rush can be written as haste)
'the north side before crossing east' is the wordplay.
'the north' says the letters should be written in reverse (in a down clue, letters go up or 'northward').
'side' suggests removing the centre (I've seen 'sides of' mean this (only the letters on the sides remain)).
'before' becomes 'erst' (archaic term for formerly or long ago).
'crossing east' becomes 'sah' (I am not sure about this - if you are sure you should believe this answer much more).
'erst' with its centre removed is 'et'.
'et'+'sah'='etsah'
'etsah' written backwards gives 'HASTE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for haste that I've seen before include "Hurry, urgency" , "furious activity" , "Urgency of action" , "go at speed" , "Expedition" .)