The Barclays Center sends notice regarding February events. No crowd estimates, but "exterior impacts" for circus, MMA
On Tuesday, 1/24/17, however, the arena's new VP for Community Relations, Roland Guevara, circulated the February Community Notice pictured below.
Note the "expected exterior impacts" regarding several circus performances and the UFC (Ultimate Fighting Championship) mixed martial arts (MMA) event on 2/11/17.
While the message says "Please standby for more details," it's a good bet that such impacts include crowds gathering on the arena plaza, with merchandise sales and--at least for the UFC--perhaps some chanting or otherwise aggressive behavior.
On Wednesday morning, I asked Guevara by email if that was a policy change, or if it was because there are no non-ticketed events scheduled. (The document does say it lists "all February events.") I haven't heard back.
Also, in contrast with those previous event calendars, it does not list expected attendance, which provides guidance. I asked if they planned to list expected attendance or otherwise provide guidance about potential crowd size. If I learn more, I'll post an update.