Changed ends every six balls (by accident?) (3,4)
I believe the answer is:
run over
'changed ends every six' is the definition.
I can't judge whether this defines the answer.
'balls by accident?' is the wordplay.
'balls' becomes 'over' (I've seen this in other clues).
'by' says to put letters next to each other.
'accident?' becomes 'run' (I can't explain this - if you can you should give a lot more credence to this answer).
'over' put after 'run' is 'RUN OVER'.
Can you help me to learn more?
(Other definitions for run over that I've seen before include "Knock down (a pedestrian) - carry out a rapid check" , "Knock down and crush with vehicle" , "Flatten with a car" , "Take too long" , "Hit with a car" .)