A Thanksgiving meal that would be routine any other year could result in a 911 call and a fine, warns Boston Mayor Marty Walsh.

As Boston hit an average of 224 new cases of COVID-19 a day, Walsh announced a range of new metrics the city will use for measuring the pandemic's growth. He also threatened to enforce the city's ban on more than 10 people gathering indoors for the upcoming holiday.

"We don't want to do this, but as the holidays go on, people are going to call 911," Walsh said, adding that police would show up and notify the city's Inspectional Services Department, which will issue fines.

"I mean, that's the last thing I want to do on Thanksgiving," Walsh said. "And I know people aren't agreeing with what I'm saying right now. But the numbers aren't lying."

Walsh also had a request for the college students who would ordinarily go home for the Thanksgiving holiday.

"We have asked colleges and students not to do that this year," he said. "If you go home for Thanksgiving, you should not be returning to Boston this semester. You should do the rest of your learning remotely."

Last week, Walsh said, the citywide positivity rate for COVID-19 tests was 9.6 percent, with seven neighborhoods above 10 percent. Walsh said East Boston, Dorchester and Hyde Park had the highest increase in cases.

Walsh announced the city will start to measure the spread of the pandemic using a new collection of six key measures - each with its own "threshold of concern," which could collectively trigger more stringent restrictions if reached.

"The goal is to give the most current and comprehensive picture of the virus that we can," he said.

Those metrics include a change in the way the city measures the rate of positive tests, to focus on the most recent test results, with the goal of getting a more accurate picture of the current situation. The city will also consider capacity in hospital intensive care units and the number of available hospital beds as well as the number of patients visiting emergency rooms who are confirmed or presumed to be infected.

Walsh emphasized the success Boston had over the summer keeping case numbers down.

"That's the work of people," he said. "That wasn't anything that any of us did in government. It wasn't the work of any of us."

The virus' spread was limited during that period, he said, by the power of residents' collective action.

"We're asking people to continue to wear masks any time you're outside your home," he said. "Wash your hands with soap and warm water as often as possible, wipe down frequently touched areas, and avoid gatherings or groups outside of your household."