Read the latest on the Las Vegas shooting with Friday’s live updates.

LAS VEGAS — Gunfire crackled, hotel guests called in noise complaints, and just like that, Jesus Campos, armed with little more than the handcuffs on his service belt, was facing a situation on Sunday that he had never encountered before as a security officer at the Mandalay Bay Resort and Casino.

Stephen Paddock, a longtime gambler who had amassed an arsenal of weapons, was firing down on thousands of people at an outdoor country music festival from his suite on the 32nd floor of the hotel.

As Mr. Campos approached the door of the suite, Mr. Paddock fired several shots through it, striking Mr. Campos in his right thigh, David L. Hickey, the president of the union representing security officers at the hotel, said on Thursday. Even after Mr. Campos was wounded, Mr. Hickey said, he helped the police locate Mr. Paddock, who did not resume his barrage of fire.

On most days, unarmed security personnel like Mr. Campos, who wears a black uniform at work, are dealing with much more mundane problems. Medical emergencies. Drunks. Arguments.

But they have to be ready for much worse. The mass shooting on Sunday night, which killed 58 people and wounded hundreds more, highlighted the dangerous side of working security in a casino hotel. Serious criminal violence is rare, but when it happens, many in the industry say, coping with it demands extensive training and preparation.

Casino security guards in Las Vegas do not fit the stereotype of whistle-blowing mall cops who chase shoplifters. Many are former police officers or military veterans who work now in plain clothes. They go through special training programs. Their forces are often led by people with experience at the highest levels of law enforcement, and they cooperate closely with the local police.

“The security in Las Vegas is tremendous,” said Don Campbell, a Las Vegas lawyer and former casino executive. “These aren’t rent-a-cops, by any stretch of the imagination.”

Even so, the mass shooting on Sunday raised new questions about how best to provide safety in a city visited by tens of millions of people a year who may be susceptible to a host of dangers. Many casino security officers are unarmed, and in many situations they are only a stopgap until the police arrive.

While a police officer typically gets around 500 hours of academy training before joining the force, most security officers at major Las Vegas casinos get 40 to 80 hours’ initial training, according to Lenny Davis, a security consultant here.

“Some of them are your normal unarmed security guards,” Mr. Davis said. “Most of the big hotels have special security units. I think you’re going to see more of that, in light of Sunday’s incident, and those guys are very well trained.”

As investigators continued to piece together what drove Mr. Paddock to kill, security officers were as visible as ever at Mandalay Bay on Thursday. They were posted at each of the three elevator banks leading to guest rooms, making sure that only those who had key cards got through. They rode around the perimeter of the property on bicycles, and guarded the barricades at the driveway to the front entrance, which remained closed. One officer was dispatched to a room occupied by reporters to tell them that interviewing employees on the property was forbidden.