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1. To break something into small pieces with great, violent force. A noun or pronoun can be used between "smash" and "up." My father went on a rampage around the house, smashing up anything he could get his hands on. The disgruntled ex-employee stole a photocopier from the office on his last day at work and smashed it up with a baseball bat in a field beside the office.
2. To cause a lot of damage or destruction to something or within some place. A noun or pronoun can be used between "smash" and "up." He was arrested for smashing up a local bar after getting into an argument with its owner. Some punks came around and smashed my car up during the night.
3. To beat someone with brutal, violent force. A noun or pronoun can be used between "smash" and "up." The gang surrounded the poor man and smashed him up so badly that he had to be hospitalized.
smash something up
to break something up; to destroy something. I hope the children don't smash any of the good china up if we use it tonight. The driver fell asleep and smashed up the car.