The board's finding came in a report released Friday by the civilian board that oversees the Toronto Police Service, the Globe and Mail reported.
"The Toronto Police Services' preoccupation with protecting the [fence] detracted from its ability to police the rest of the city and caused a policing vacuum," said the report, written by John Morden, former associate chief justice of Ontario.
During the summit, the Royal Canadian Mounted Police were responsible for handling security at the meeting site, while the surrounding fence and areas beyond it were the responsibility of the Toronto police.
The report said when Toronto police asked the RCMP to relieve them at the meeting's perimeter so they could deal with the vandalism, it took 12 hours for the federal police force to do so.
Toronto officers, the report said, stayed at the security fence when anarchists a few blocks away broke away from a march and smashed windows and burned police cars.
Toronto Police Chief Bill Blair suggested in the report officers feared the vandalism was meant to divert police away from the summit site.
The report said the federal government had chosen a site for the gathering, the Metro Convention Center, so late, Toronto police had only four months to prepare. A security operation of that scale typically would take two years to plan, Morden said.