5th UPDATE: 10:48 p.m. EDT: Tweet from Reno TV reporter Benjamin Margiott, who reports interviewing the man detained by police: The man who was detained was holding a Republicans AGAINST trump sign. I apologize for the mistake. (He had first tweeted it was a Republicans for Trump sign.)
4th UPDATE: 9:47 p.m. EDT: ABC News reporting no weapon was found.
3rd UPDATE: 9:35 p.m. EDT: Two items are important to remember right now. First, there has been NO confirmation that there was a gun. Second, according to media reports, everyone who entered the arena had to pas through a metal detector.
2nd UPDATE: 9:30 p.m. EDT: Tweet from Washington Post reporter Jose DelReal during the chaos: Massive disruption here in Reno. Armed officers jumped in. People on the floor said — & this is unconfirmed — that they saw a man pull a gun
1st UPDATE: 9:26 p.m. EDT: Information from the New York Times.
ORIGINAL POST: Working on details, but the potential of gunshots has been reported.