A few dozen people were in the plaza outside the arena, some chanting "Let Kyrie play! Let Kyrie play!" and holding signs that said "Stand with Kyrie."
Irving, a star player for the Nets, cannot play in large part because of rules unique to New York and San Francisco requiring vaccinations as a prerequisite for working. The Nets said last week that Irving would not be involved in team activities "until he is eligible to be a full participant."
Irving remains one of the few players in the league who has not yet chosen to be vaccinated.
Video posted to social media showed dozens of the protesters pushing past and over barricades and rushing towards the arena's doors. Arena officials were forced to briefly close the doors while fans were trying to get in.
A spokesperson for Barclays Center said the arena "briefly closed its doors in order to clear protesters from the main doors on the plaza and ensure guests could safely enter the arena."
No injuries were reported, and there is no reported delay to the Nets' home opener against the Charlotte Hornets Sunday evening.
Roughly 96 percent of NBA players have been vaccinated, meaning roughly 20 players, or less than one per team on average, are not.
With the Associated Press.