Knock out jockey regularly — that's strange! (5)
I believe the answer is:
kooky
'strange' is the definition.
(thesaurus)
'knock out jockey regularly' is the wordplay.
'knock out' becomes 'ko'.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'jockey' are 'oky'.
'ko'+'oky'='KOOKY'
'that's' is the link.
(Other definitions for kooky that I've seen before include "Strange - eccentric" , "Rum" , "nuts" , "Crazy and eccentric" .)