LONDON — You know that feeling you get when a soccer pitch or a football gridiron stretches across the outfield at Yankee Stadium? It’s a sort of athletic anachronism, and it takes some getting used to.

That’s how Londoners likely will feel while watching the Giants and Rams play on Sunday in the first NFL game at Twickenham Stadium, the physical and spiritual home of English rugby and the national team. Only worse. Their sacred ground will be graffitied with stripes and hash marks, their green pasture emblazoned with a painted NFL shield, and their clean white goalposts replaced with the garish day-glow yellow ones of American football. All to make way for a sport that has roots in rugby, but hardly acknowledges its own ancestry.

And all those dreadful helmets and shoulder pads! Where is the honour?

Twickenham is the Wrigley Field, Lambeau Field, and Madison Square Garden of the rugby world here, all rolled into one 82,000-seat edifice (which will hold 75,000 on Sunday because of NFL specifications). It was built in 1907, raised from a flood plain in the southwest corner of the city with earth excavated from the construction of one of London’s Underground lines. The British army grazed and trained cavalry horses there in World War I. It became a civil service depot in World War II, complete with an area ready to treat patients in the event of a poison gas attack on the city.

It withstood those two wars, a century of sporting events, and countless expansions from the original 18,000-fan capacity. It has charm, legacy, and its own identity. Now, it faces American football and a brigade of players who, for the most part, have no clue about the significance of where they will be.

“Have you ever seen a rugby match?” Giants linebacker Jonathan Casillas was asked by an eager British reporter on Friday.

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“No, I have not,” he said with a smile.

What do you know about Twickenham?

“Not too much.” Again, though, with a smile.

Wide receiver Victor Cruz admitted his knowledge of the sport consists mostly of a recent viral video that featured a robust 8-year-old boy galloping over and through undersized opponents. Turns out there wasn’t much rugby being played when Cruz was growing up in Paterson, New Jersey.

“At least we didn’t call it rugby,” he said of the rough games he played in the neighborhood streets.

Eli Manning at least has enough basic knowledge of the sport to make a comparison to his own.

“Those guys are athletes, and tough, and hopefully I won’t be taking as many hits as they take in a rugby game,” he said. “I have a lot of respect for the game of rugby and I’ve enjoyed watching it a few times on TV. It’s an honor just to be here and be able to play in their facility.”

Cruz said he doubted anyone on the Giants had even seen a rugby game, but there was one player who at least spoke with the enthusiasm and reverence of someone who has.

“I can’t wait to get there,” wide receiver Odell Beckham Jr. said. “See the atmosphere and the stadium. It’s going to be like a dream come true. Hopefully I can get out there and just have fun. Embrace it all and enjoy every moment. You don’t get too many like that. I’m looking forward to it.”

Even then, though, he had to mix his sports metaphors while trying to describe his expectations.

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“Hopefully,” he said, “it’s as loud as it is when you have the FIFA [video game] turned all the way up and you score a goal or something.”

That’s soccer, not rugby. Oh well. Close enough.

Sorry, London.