Pinball foul (4)
I believe the answer is:
tilt
'pinball foul' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tilt that I've seen before include "Slight inclination" , "Inclination, joust" , "Tip to one side" , "Lean, slope" , "Slope; joust" .)