Mate astride wild steed needs support (8)
I believe the answer is:
pedestal
'support' is the definition.
(pedestal is a kind of support)
'mate astride wild steed' is the wordplay.
'mate' becomes 'pal' (I've seen this before**).
'astride' is an insertion indicator.
'wild' indicates anagramming the letters.
'steed' with letters rearranged gives 'edest'.
'pal' going around 'edest' is 'PEDESTAL'.
'needs' is the link.
(Other definitions for pedestal that I've seen before include "Base supporting column" , "Plinth, base" , "Supporting column of a washbasin" , "Base supporting a statue" , "Statue's base" .)