Protest and say, with outline of scowl, "I'm in pain!" (2-4)

I believe the answer is:

go-slow

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'protest' is the definition.
(I know that go-slow is a type of job action)

I don't understand the rest of the clue.

(Other definitions for go-slow that I've seen before include "Work-to-rule" , "Type of industrial action" , "Form of industrial action" .)

I've seen this clue in The Independent.

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