1.
If someone beats up on a person or beats on them, they hit or kick the person many times. ( AM )
He beat up on my brother’s kid one time.
PHRASAL VERB : V P P n , also V P n
2.
If someone beats up on another person, they threaten them or treat them unkindly. ( AM INFORMAL )
She had to beat up on every customer just to get the bills paid.
PHRASAL VERB : V P P n