An idiot cycling with Alf (7)
I believe the answer is:
halfwit
'an idiot' is the definition.
(both can mean a stupid person)
'cycling with alf' is the wordplay.
'cycling' is an anagram indicator.
'with'+'alf'='withalf'
'withalf' is an anagram of 'HALFWIT'.
(Other definitions for halfwit that I've seen before include "Being stupid" , "Charlie?" , "One only 50% all there?" , "Mug" , "Idiot" .)