Tries to make one admit they’re setbacks (6)

I believe the answer is:

knocks

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'tries' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

I don't understand the remainder of the clue.

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(Other definitions for knocks that I've seen before include "Raps; criticises" , "Strikes with a sharp blow or finds fault with" , "Gentle taps" , "Hits" , "Bangs on door" .)

I've seen this clue in the Evening Standard.

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