Bank's free cycling (4)
I believe the answer is:
reef
'bank's' is the definition.
(I've seen this before)
'free cycling' is the wordplay.
'cycling' indicates an anagram.
'free' is an anagram of 'REEF'.
(Other definitions for reef that I've seen before include "Rocks in shallow water - kind of knot" , "Chain of rocks underwater" , "Submerged ridge of rock or coral near the surface" , "Main bank" , "Atoll protector" .)