I was in one of the safezone containers at splatoon yesterday and there was a few guys firing inside, barrel socks off. Luckily the mags was out and the chambers empty but as they was rentals, that was definitely due to luck rather than them checking it was clear etc (Not that it excuses it) admittedly they was taken care of by a marshal, but still not ideal.
Prior to the barrel sock rule, somebody was shot in the safe zone during an airsoft event which is why I think it was introduced. Personally I'm a huge fan of it as it does eliminate a lot of the risk, but only if people use their due diligence and actually adhere to the rules set by the site.