The various vax requirements now apply to everyone in the stadium except players. Seems a bit unfair yes, but the players had their own negotiations and their union was able to successfully fight off a vaccination mandate.
FYI, the same goes for the NBA players as far as I know. Everything I’ve read on them recently has said that a vaccine mandate for players is a non-starter. They will not agree to it. So I’m not sure how MSG or Barclay’s is going to attempt to enforce that, beyond cancelling games at those venues altogether.
edit: link about the NBA (sorry for the google link): https://www.google.com/amp/s/www.espn.com/nba/story/_/id/32208394/sources-nba-players-required-get-covid-19-vaccination%3Fplatform%3Damp