Free half of beer for the equestrian (5)
I believe the answer is:
rider
'the equestrian' is the definition.
(thesaurus)
'free half of beer' is the wordplay.
'free' becomes 'rid' ('rid' can be a synonym of 'free'**).
'half of' suggests halving the letters.
'beer' cut in half is 'er'.
'rid'+'er'='RIDER'
'for' is the link.
(Other definitions for rider that I've seen before include "qualification" , "Person on horse" , "Possibly cavalier" , "knight" , "recommendation made in court" .)