Throw off course, breaking rule that’s applied to cycles (10)
I believe the answer is:
derailleur
'to cycles' is the definition.
I can't tell whether this defines the answer.
'throw off course breaking rule that's applied' is the wordplay.
'throw off course' becomes 'derail' (**).
'breaking' means one lot of letters goes inside another.
'that's applied' indicates anagramming the letters.
'rule' anagrammed gives 'leur'.
'derail' placed inside 'leur' is 'DERAILLEUR'.
(Other definitions for derailleur that I've seen before include "Cycling gear" , "may go on bike" .)