Or maybe while they are engaging the perps, back-up will be coming with the rifles.
Who would be back-up? From what i see, the security employees are already spread thin, handling complaints of rowdy customers, guarding the carts used to collect the money from slots, accompanying the chips as tables are replenished, etc. i don't know if there are enough extra guards to run & grab the rifles.
Anytime there is a disturbance, security's number one job is to protect the gaming areas they are assigned to. i don't think someone on the other end of the casino will leave their area unguarded -- vulnerable to theft -- in order to grab rifles for security personnel engaging criminals on the other end of the casino.
i saw a woman at Circus Circus suffer a seizure while at the BJ table. One guard stood over her while a second guard watched the table -- i suspect to make sure the chips didn't walk off. An incident like that could be staged hypothetically to distract employees while someone grabs a fistful of chips or does something else shady. The woman was thrashing on the floor for at least a couple of minutes until someone came to her aid. Nobody -- not a customer and not an employee -- bothered to help her by placing anything between her teeth or holding her head to prevent injury.
That kind of tells me the staff has been instructed to do as they are trained, which means don't get distracted from protecting the casino's money.
Maybe after the mass shooting at the concert policies and security staff sizes were upgraded? i just know what i saw that time at Circus Circus and other less serious situations where security had to get involved.