The 2008 Supreme Court Heller v. DC decision (the most clearly affirming case of the private citizen's right to keep and bear arms in the history of the country) foreshadows how such a challenge would end. Even in Scalia's opinion he states...
"The Court's opinion, although refraining from an exhaustive analysis of the full scope of the right,...should not be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms."
While the Supremes clearly chisels out the right of the private citizen to have a gun immediately accessible and loaded in their home, they leave some latitude to the District for licensing and limitations with respect to where such weapons may be kept or taken.
Arenas had no license, nor do the laws of the District of Columbia allow for weapons to be carried in such places as sporting arenas. Gilbert's chances of prevailing with such an argument are virtually non-existent.
Lastly, the last collective bargaining agreement between the player's association and the NBA expressly forbids the possession of firearms in NBA arenas, practice facilities or at NBA sponsored events and activities.
I don’t see the “latitude” for licensing owners which you mention. “...laws imposing conditions and qualifications on the commercial sale of arms....” would mean that the city can regulate gun shops.
Also, “...schools and government buildings..” implies PUBLIC buildings. The Verizon Center is private property.
Your mention of the NBA’a collective bargaining agreement is totally irrelevent to the “criminal charges” aspect of the case. In fact, I had already stated my opinion on THAT issue when I wrote: “As for the league/team rules/punishment, IF there is a “no-gun” clause in his team/NBA contract, or if the league or the team have previously established “no-gun” rules for the locker-room(s), then he should just face his team/NBA punishment like a man.”