Now with a little time to respond, I'll elaborate on my last post.
I did not mean to insinuate that any sport could nullify federal, state or local laws. Obviously that is not the case.
Concealment without permit; I equate it to something along the lines of, you tackle someone to the ground on Main St. that = assault. If you tackle someone on the football field, within the rules, no problem. I suppose that if one of these matches were to be raided by the police, they could charge any or all of the 30+ competitors, but that seems unlikely. Some of these matches even have local LEO as participants. Also, IDPA is a global association with matches held in every state in the US as well as more than fifty foreign countries. Exposure is fairly high.
As far as magazine capacity; the Maryland Firearms Safety Act of 2013 only made it illegal to buy, sell or transfer magazines with capacity over 10 rounds after October 1, 2013. Everything prior was grandfathered in. As long as you leave with the same items you entered, no problem. In states where there is a complete ban on magazines of certain capacity, there are no exceptions. Those matches have to be run with certain rule modifications.