Move on horseback, approaching hurdles (2,6)
I believe the answer is:
up sticks
'move' is the definition.
(to up sticks is to move house)
'on horseback approaching hurdles' is the wordplay.
'on horseback' becomes 'up' (up can mean up on a horse).
'approaching' says to put letters next to each other.
'hurdles' becomes 'sticks'.
'up'+'sticks'='UP STICKS'
(Other definitions for up sticks that I've seen before include "Make off" , "Move away without warning" , "Move house(colloq.)" .)