TAUNTON (CBS) – A Halloween prank last year could prove to be very costly to the Taunton school system.

Last October, a teacher at Taunton High School asked a 15-year-old student to answer a knock on the classroom door. At the door was a man in a mask and carrying what appeared to be a running chainsaw.

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The student then jumped back, tripped and fractured a kneecap.

“He was extremely terrified. He just wasn’t expecting something like that,” said Tom Dussault, an attorney who represents the teen’s family.

WBZ NewsRadio 1030’s Mark Katic reports.

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The boy had surgery, spent four months of crutches and is enduring ongoing rehabilitation.

“He continues to treat with a surgeon in the Boston area and we don’t know what the final outcome will be,” said Dussault.

Dussault said the family is preparing a lawsuit, but is exploring ways to avoid a trial and do better than the $100,000 cap when suing city employees.

The Taunton city solicitor’s office confirmed the pending lawsuit but would not discuss last year’s incident.

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Any potential trial would begin in the spring.