One on the wagon making athletic movement (9)
I believe the answer is:
cartwheel
This could be a double definition.
'one on the wagon' is the first definition.
(I've seen this before)
'athletic movement' is the second definition.
'cartwheel' can be an answer for 'movement' (I have seen 'Acrobatic movement' mean 'cartwheel' so perhaps 'movement' could also mean 'cartwheel'). I am not sure about the 'athletic' bit.
'making' acts as a link.
Can you help me to learn more?
(Other definitions for cartwheel that I've seen before include "Athlete's revolutionary act" , "to go on the wagon" , "Acrobatic movement" , "liable to get into a rut?" , "Handspring" .)