The demonstrators were chanting "let Kyrie play" after NBA all-star Kyrie Irving was sidelined earlier this month because he refused to get protected against the coronavirus.
On Sunday, hundreds gathered outside the stadium in protest while a smaller group pushed through metal barriers and chanted as they charged toward the entrance.
A shaky video of the scene, posted by FreedomNews.tv, showed security guards trying to push away the angry crowd as they tried to enter the building.
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Security locked the building to block more protestors from infiltrating.
Some protestors flew banners as others shouted through blow horns, banged on the building's glass doors, chanted "we will not comply" and waved American flags.
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The rally came after Irving, 29, was told he would need evidence of at least one vaccine shot to play in his own arena, Barclays Center, or use at the team facility in Brooklyn.
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He stands to lose about half his nearly $35million salary by rejecting the shot but previously said he doesn't regret his decision.
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"So what? It's not about the money," Irving said. "It's not always about the money. It's about choosing what's best for you. You think I really want to lose money?"
He would have played the season's first home game Sunday if he followed the mandate, infuriating fans who thought he shouldn't have had to pick between the vaccine and his career.
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One fuming protestor accosted fans entering the stadium ahead of the game against the Charlotte Hornets.
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"Are you guys OK with Kyrie Irving not being able to play because he refuses to be a slave? Are you guys OK with being slaves of the system? Giving up your bodies to be lab rats just so you can go to a restaurant; just so you can go to a basketball game?
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"Do you even know what's in that injection? Do you even care? Do you give a Sh**? You're all lab rats. You have zero idea what's in that injection."
It wasn't instantly apparent how police and security officers dispersed away from the mob, but the Barclay Center said in a statement that the game was not affected.
"Barclays Center briefly closed its doors today in order to clear protestors from the main doors on the plaza and ensure guests could safely enter the arena,' the statement said. 'Only ticketed guests were able to enter the building, and the game proceeded according to schedule."
In late September, the NBA reported a 95 percent vaccination rate among players.
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