Wheel shaft is left in the chopper (4)
I believe the answer is:
axle
'wheel shaft' is the definition.
(I've seen this before)
'left in the chopper' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in the' means one lot of letters goes inside another.
'chopper' becomes 'axe' (something which chops).
'l' inserted inside 'axe' is 'AXLE'.
'is' is the link.
(Other definitions for axle that I've seen before include "Mandrel" , "Rotating spindle" , "need of wheeled cart?" , "Rod bearing wheels" , "It's pivotal" .)