Study racehorse’s record and fit in (7)
I believe the answer is:
conform
'fit in' is the definition.
(thesaurus)
'study racehorse's record' is the wordplay.
'study' becomes 'con' (I've seen this before).
'racehorse's record' becomes 'form' (form refers to the past performances of a horse).
'con'+'form'='CONFORM'
'and' is the link.
(Other definitions for conform that I've seen before include "Match" , "Keep to rules or general custom" , "Fall into line" , "Follow the crowd" , "Follow the herd" .)