In one-on-one matches, members of Gladiators NYC wear helmets, chain mail and full armour weighing up to 45kg.

They bash each other in the head with real weapons and violently kick, punch and throw each other in the dirt, using full-contact mixed martial arts techniques in three one-minute rounds.

In melee matches, up to four knights fight to the finish, until one is left standing.

Gladiators NYC is the flagship programme for free martial-arts and fitness non-profit Santa’s Knights, founded by 40-year-old Damion DiGrazia eight years ago.

DiGrazia’s path to teaching martial arts to children and aspiring knights is an unusual one, from the United States Air Force to Columbia University, to a master’s in finance at Harvard University, and then as a management consultant at Morgan Stanley.

“It was really like I had arrived,” he says, standing outside of his former workplace on a sweltering August day.

But as he sat there in his big glass tower, he realised his interest in money – the driving motivation behind working at one of the top three investment banks in the world – was missing.

“If money doesn’t motivate you, then what do I do? I was like, ‘Helping people, I like to help people.'”

For DiGrazia, the way to do this was to start a non-profit that offers free martial-arts and fitness classes for all.

“We just hit the core of it, which is to be healthy and do fitness,” he says. “And when you do more fitness, you eat more healthily. You change your lifestyle, and now we’re saving lives.”