I'm not from Boston, so I don't know the exact meaning of the phrase.
However, I'm fairly sure it does NOT mean "hold up", which means "rob (usually with a weapon)".
I hope someone from Boston or the northeast of the US will reply with a good "translation" of this term!
(NOTE: This is a great example of the different regional variations of American English - I'm from Nevada, and Good Will Hunting was set in Boston, Massachusettes on the other side of the country!)
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