Follow a series of races to finish (6)
I believe the answer is:
attend
'follow' is the definition.
(thesaurus)
'a series of races to finish' is the wordplay.
'a series of races' becomes 'att' (I've seen this in other clues).
'to finish' becomes 'end' ('end' can be a synonym of 'finish').
'att'+'end'='ATTEND'
(Other definitions for attend that I've seen before include "Pay heed" , "Concentrate carefully" , "Be present or appear at" , "Escort (someone)" , "Completed" .)