Quick answer
A good ruler separates the harmful from the rest and deals with them decisively. The image comes off a threshing floor.
Read both lines
The verb is the same winnowing word used of the king's eyes at verse 8, so the chapter is finishing a thought it started eighteen verses earlier: royal justice is fundamentally about separation. The second line supplies the heavier half of the process. A threshing wheel was a weighted roller dragged over cut grain to break the husk from the kernel, which is not decorative violence but the ordinary machinery of harvest. Applied to a court it means something exact and limited: the useful is kept, the useless is broken off, and the point of the operation is what survives it. That limit matters for reading the verse three lines later, which returns to the same subject. Justice here has an object, and the object is the community left standing afterward.
Related: Proverbs 20:8 · Proverbs 20:28 · Proverbs 20:30 · Proverbs 25:5
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.