Eyewitness News saw families with small kids, a pregnant woman, and scores of everyday basketball fans who were forced to shove their way through the gauntlet of protesters and into the arena.
Hundreds of police officers struggled to control the crowds, but with obvious orders to use restraint, they were outmatched from the start.
Once the game started, the crowd moved off of the plaza, and took over the busy intersection of Atlantic and Flatbush. Some taunted stone-faced police officers.
One fire truck on the way to a call had nowhere to go, and came to a stop. As did thousands of commuters.
Later, the crowd flooded down the escalators of a Target across the street, where they staged what they called a "Die In" to protest the death of Eric Garner and the Grand Jury's decision not to indict the officer whose alleged chokehold caused his death.
Through it all, inside the Barclays Center, if the objects of all this attention had any idea what was going on outside, William and Kate showed no sign of it. Of course they got to use a different door.
As for some, Monday's royal visit became a royal pain.
Earlier in the day, New York City Councilman Jumaane Williams held a die-in with 22 council members at City Hall around noontime.
Council members marched into the Council Chambers chanting "Hands up, don't shoot" and singing "We Shall Overcome."
Williams and City Council Speaker Melissa Mark-Viverito were both wearing "I can't breathe" T-shirts and red arm bands.
Earlier, a demonstration was held on Staten Island when about a dozen activists block traffic on the eastbound Staten Island Expressway at Clove Road.
They stopped cars approaching the Verrazano-Narrows Bridge at about 9:30 a.m., but moved off the roadway when police arrived and traffic began moving again.
The NYPD said that the protesters got on a bus and left.
Video courtesy Julian Guerrero
The group said they wanted to block the highway for seven minutes to symbolize what they said was the seven minutes that the NYPD and EMTs were recorded not providing medical care to Garner after the apparent chokehold by Officer Daniel Pantaleo.
It is the latest in a series of mostly peaceful demonstrations following the grand jury's decision.
Hundreds of protesters staged a "Choke-In" inside Grand Central Terminal on Saturday. The rally remained peaceful even after the group headed out onto city streets with a handful of police officers alongside them.
Over 200 people were arrested in protests last Thursday night.