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Related to round on: round games
To suddenly attack, berate, or show hostility toward someone, especially verbally. I know he seems friendly, but he'll round on you in an instant if you disagree with him. I was really taken aback when Sally rounded on me because of what I said. It was just a joke, after all!
Turn on, assail, especially verbally. For example, They all rounded on Jake for not upholding the party line. [Mid-1800s]
To assail someone suddenly; turn on someone: The entire group rounded on me when I questioned their motives.