Walk out in opposition to arrest (3,2)
I believe the answer is:
run in
'arrest' is the definition.
(I've seen this before)
'walk out in opposition' is the wordplay.
I cannot really see how this works, but
'in' is within the answer.
The remaining letters 'run' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
(Other definitions for run in that I've seen before include "Dispute" , "final stages of race" , "Informally, take into custody - on the trot?" , "Disagreement, fight (colloq.)" , "Skirmish" .)