Whirling motion of Merckx maybe (4)
I believe the answer is:
eddy
'whirling motion' is the definition.
(type of whirlpool)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for eddy that I've seen before include "Water circulating" , "Turner at sea" , "Small circular movement of water" , "Circular movement of air" , "Little swirl in water" .)