"Set right pace finally when chasing" said running coach (8)
I believe the answer is:
disabuse
'set right' is the definition.
(thesaurus)
'pace finally when chasing said running coach' is the wordplay.
'finally' indicates one should take the final letters.
'when chasing' says to put letters next to each other.
'running' is an anagram indicator.
'coach' becomes 'bus' ('bus' can be a synonym of 'coach'**).
The last letter of 'pace' is 'e'.
'said' with letters rearranged gives 'disa'.
'disa'+'bus'='disabus'
'e' put after 'disabus' is 'DISABUSE'.
(Other definitions for disabuse that I've seen before include "Rid (one of wrong idea)" , "put right" , "Free somebody from an erroneous belief" , "Rid someone (of a mistaken idea)" , "Undeceive, set right" .)