SUNBURY-ON-THAMES, England -- Conor Gilsenan isn't a small man.

He stands 6-foot-3 and weighs 229 pounds. He's the same height as Arizona Cardinals wide receiver Larry Fitzgerald and weighs 11 pounds more. Gilsenan doesn't look imposing by most standards, but he's tough -- he's plays in the back row for the London Irish Rugby Club -- and has the size to be an NFL player. There are 53 players in the league who are 6-3, according to ESPN Stats & Information. Of those, 31 weigh less than him; 21 weigh more. One, Denver Broncos receiver Demaryius Thomas, weighs the same.

But as Gilsenan stood on the sideline of one of the Irish practice fields last week watching the Cardinals prepare for their game at London's Twickenham Stadium -- it would turn out to be a shutout loss to the Los Angeles Rams -- he was in awe of the size of some of the players in front of him.

"Let's put it this way: I wouldn't like to fight any of those NFL players, particularly the big blokes," Gilsenan said with a chuckle.

With Arizona having spent a few days sharing the Irish facilities, the two sports were on full display. But there was one major difference: American football players wear pads. Rugby players don't.

So, who's tougher?

"It's a tough question," Gilsenan said. "I can't really give you a straight answer.

"Some of the injuries those guys get are horrific. It just looks awkward and nasty sometimes because the collisions are so fast. But we go through a lot and we play a lot of games. It's a grind, the season."

Topsy Ojo, a winger for the Irish, said for as similar as rugby and football are -- he believes if you watched both simultaneously they'd be tough to decipher -- they're vastly different.

Football is full of short spurts. Plays last just seconds and then players have time to rest.

Rugby is a continuous sport with plays lasting anywhere from two to five minutes.

"We're endurance athletes," said Gilsenan, who was taken aback by how disjointed NFL games were when he saw one live for the first time.

Before taking in his first NFL game, Gilsenan was used to seeing the sport through TV highlights. To him, all the plays looked like they flowed together. That wasn't the case in person.

Because of how football starts and stops, Ojo and Gilsenan think the plays are more intense and the collisions more serious than in rugby.

After watching the Cardinals practice in pads, neither changed their minds about playing a sport in which they wear little, if any, protection.

"No, no, I'm not conditioned to [wear pads]," Ojo said. "The physical part of the sport is something that you have to be comfortable with and enjoy."

Gilsenan didn't think the idea of protecting his body with padding would help.

"If someone put that helmet on me and those pads in rugby, I don't see how it would help, to be totally honest," he said. "It's just a weird concept. To me, that helmet wouldn't help, but I'm sure it does. The pads, it's just like an extra armor.

"We don't have the luxury of that. We have the foam paddings, but it's normally just to protect the ears aesthetically. And shoulder pads help the elbows a little bit. Big men, big collisions. They probably need more pads."

The idea of playing without pads, however, didn't interest some of the Cardinals.

"I played sandlot football growing up a lot," safety Tyrann Mathieu said. "But we were 80 pounds back then, so I can't imagine somebody, 240 pounds, hitting me without any pads on. I'm pretty sure I'd be on IR [injured reserve]."

But right guard Earl Watford could see himself hitting someone his size without pads.

"It's essentially the same thing, right?" he said. "A little different."

The Irish have borrowed a few concepts from their American visitors this year. Before the Cardinals practiced there, the New Orleans Saints did. The Saints had a DJ playing music before practice when they were in London a few weeks ago. The sun was shining and the atmosphere has a "feel-good factor" to it, Gilsenan said. So when the weather is good before practice, the Irish now play music, as well.

"It gives you a bit of a lift before training," Gilsenan said.

But the NFL can learn something from rugby, Fitzgerald said.

"Those guys have much better technique than we have," he said. "You see them tackle, they tackle proper -- heads up, wrap and run. They have less issues than we do. We could learn a thing or two from the way they play."

Rugby players are taught from a young age how to tackle properly, Ojo said.

"That's maybe one thing we're definitely ahead [in]" compared to the NFL, he said. "Otherwise it's unsafe for you and the guy you're trying to tackle and you'll end up missing a lot of tackles, as well.

"Technically, especially at the elite level, you have to be good at that. Otherwise your defense will just suffer. I know it's something the NFL has been trying to get to grips with more recently by teaching young guys to tackle properly, because if you do that, it's an effective weapon."

As in the NFL, injuries are a way of life in rugby.

Ojo and Gilsenan both said the only time they're 100 percent healthy is the day before the season. Both were healthy last week, but their injury résumés were something NFL players would cringe at. Gilsenan broke down his ailments by sides of his body. He's had operations on his right ankle, two on his right knee, hip, left shoulder and right shoulder, and has suffered from a broken scapula. Ojo had his eye socket surgically repaired as well as operations on both shoulders and right knee.

"Not too bad in 14 years," he joked.

Gilsenan, however, added he's had two or three concussions. Head injuries have been a major issue for rugby, Ojo said, but the sport has worked to prevent them, like the NFL has. Rugby, like football, has concussion protocols. If there are suspicions of a head injury, the player gets checked and assessed by an independent observer. If he's cleared, he can return. If not, he's removed from the game and enters the postgame protocol. If there's no delayed reaction during the weeks after the injury, he's not allowed to return, Ojo said.

Even though both players would like to try their hand at American football -- Ojo didn't hesitate when asked if he'd like to play -- they don't have a desire to leave rugby for good.

Ojo is a New York Jets fan, a result of having family in New Jersey. Watching the NFL games in London over the years has piqued his interest in the sport, and having the Cardinals and Saints practice at the Irish's facility has given him a front-row seat.

That doesn't mean he'd join one of the teams in Great Britain, where football has been growing. However, Ojo doesn't see the sport spreading faster or as having the same cultural impact as rugby or soccer unless there are grass-root movements in the sport.

And while Gilsenan would "love to give it a crack," he's not sure what position he'd play.

"My game is all endurance," he said. "There's no aspect for that in football, so I'd probably be useless."