Pace kept by strongest riders (6)
I believe the answer is:
stride
'pace' is the definition.
(I know that pace can be written as stride)
'kept by strongest riders' is the wordplay.
'kept by' indicates the answer is hidden within the clue.
'STRIDE' is hidden in the letters of 'strongest riders'.
(Other definitions for stride that I've seen before include "Step out energetically" , "jazz piano-playing" , "Long step of direst kind" , "Move with long steps" , "Long pace" .)