Heading north, astonish fans
I believe the answer is:
nuts
'fans' is the definition.
(both can mean enthusiasts)
'heading north astonish' is the wordplay.
'heading north' shows that the letters should be reversed in order.
'astonish' becomes 'stun' (I've seen this in another clue).
'stun' in reverse letter order is 'NUTS'.
(Other definitions for nuts that I've seen before include "Nibbles" , "Crazy (from Brazil?)" , "Fruit with edible kernel" , "Mad; seeds" , "Heads - fans - fruit" .)