(CNN) — “Help!” yelled a flight attendant as she grabbed a knife-wielding man and wrestled to pin the knife against her hip. “I need help!”

Then the struggle stopped. “Alright, let’s do it again,” the instructor said. “Reset!”

The knife was made of rubber. The man was a fellow flight attendant. They struggled not in a life-or-death brawl inside a cramped airplane cabin, but instead practiced at a padded gymnasium with their federal air marshal instructors.

The eight flight attendants in this Miami-area class were among hundreds the Transportation Security Administration plans to train this summer and fall in self-defense skills. It is restarting the half-day course first developed in 2004 that was recently put on hold due to the coronavirus pandemic.

The skills include how to strike, stomp and subdue a violent attacker — a scenario these flight attendants said they hope to never encounter.

Amid the return to air travel this year, the number of unruly and violent passengers is spiking. More than 100 incidents were reported to the Federal Aviation Administration in the last week — for a total of more than 3,600 so far this year.

Flight attendants are taught a set of de-escalation techniques to handle difficult passengers — the ones who won’t stow a tray table or who insist an oversize suitcase fit in the bin last time.

But they say the defiance and violence that accompanies this return to travel is testing those skills.

“You get on a plane full of people and some of them are not very happy and you just never know what’s going to happen,” said Carrie, a flight attendant who took the class as she returns to work after a pandemic-related leave of absence.

“It’s just more imperative that we take care of ourselves and take care of our passengers because people are anxious, and they’re upset, and they’re frustrated, and sometimes that comes out inappropriately,” she said. (Carrie asked CNN not publish her last name because she was not authorized by her airline to speak publicly.)

Learning last-resort tactics

Instructors taught a range of skills, from a defensive stance to blows that can be delivered on a would-be hijacker desperate to commandeer the plane.

One instructor used a mannequin to demonstrate a last-resort method of going at an attacker’s eyes.

“You are going to possibly die. You need to defend yourself at all costs,” he said. (CNN agreed to not identify the instructors because they are active-duty federal air marshals whose work on aircraft is done undercover.)

Most encounters will never rise to that level. But Federal Aviation Administration summaries of more than 40 onboard incidents in recent months show the brazen dissent flight attendants are tasked with addressing.

In one instance, the FAA said a passenger “tried to open the cockpit door, repeatedly refused to comply with crew members’ instructions, and physically assaulted a flight attendant by striking him in the face and pushing him to the floor.” After crewmembers restrained the passenger in plastic handcuffs, he “freed himself from one of the handcuffs and struck the flight attendant in the face a second time.” The passenger was not named in the report.

In another instance, the union representing Southwest Airlines flight attendants said a passenger’s punch knocked out two of a flight attendant’s teeth.

About three-quarters of the incidents reported involve passengers violating or repeatedly defying the federal requirement to wear a face mask when onboard a plane. Another common theme is alcohol — so much so that many airlines have withheld alcohol service on flights.

‘I don’t ever want to use any of this’

Sara Nelson, international president of the Association of Flight Attendants, said a small set of passengers are “treating flight attendants as punching bags, and they’re doing that verbally and physically.”

“We are finding that our jobs are harder than ever,” Nelson said. “Conflict is rising very quickly. When we can’t get to that and diffuse that because we have so much going on … problems can become big very quickly.”

Back at the training, Donna O’Neil was practicing an elbow strike that she could use if a violent passenger charges her in the aisle or galley from behind. She has 47 years of experience and said she is “pretty good at calming things down.”

“I don’t ever want to use any of this,” O’Neil said after the training. “But if I had to, I certainly feel much more confident.”

An air marshal supervisor, Noel Curtin, walked in to watch some of the training, and said he hopes crew members walk away with that type of confidence.

“We’re not omnipresent, so it’s important to have crew members able to deal with individual incidents on the aircraft,” Curtin said later in his office.

“There’s no backup at 30,000 feet.”