beat up
beat up {v.}, {informal}
To give a hard beating to; hit hard and much; thrash; whip.
When the new boy first came, he had to beat up several neighborhood bullies before they would leave him alone.
- Used with "on" in substandard speech.
The tough boy said to Bill, "If you come around here again, I'll beat up on you."
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Source: A Dictionary of American Idioms