“I didn’t get to see much of the Six Nations,” HR McMaster says with a dry laugh. “I was kinda busy.”

Until 22 March, five days after Ireland beat England to win a grand slam, McMaster was Donald Trump’s national security adviser. Two days after his resignation from that hot seat, Washington still aflame with the story, he was seen in the crowd at Annapolis as Army beat Navy at rugby. The general was a politico for a year but in rugby union he’s a lifer. The night before our conversation, which he conducts from the road, a bunch of old team-mates gathered to send him off from the capital.

McMaster hasn’t spoken publicly about his time in the White House, which lasted 13 months after he replaced another general, Michael Flynn, and which produced reports of clashes with Trump over the Iran nuclear deal, North Korea, Russia and other key policy issues. He was replaced by Bush-era UN ambassador John Bolton, not a general – or a known rugby player – but a notably more hawkish presence.

The rules of engagement for our interview mirror the way McMaster has spent his time since leaving Trump’s employ: no politics, plenty of rugby. On Saturday in Philadelphia, he will present the Pete Dawkins Trophy to the winners of the Collegiate Rugby Championship sevens. He’ll also keep an eye on events back in DC, where Wales will play South Africa at RFK Stadium.

A good rugby team always comes together on and off the pitch to support a fallen team-mate

His background in the game has been reported. A widely read New Yorker profile mentioned it and in March, an NPR correspondent even sought to deploy it to explain ructions at the White House: “Anybody who knows any rugby players knows those people tend to be relentless and aggressive.” The thought was overly broad but it contained a kernel of truth.

McMaster has never been afraid to challenge accepted thinking. He turned his PhD into Dereliction of Duty, a seminal book on the US military failure in Vietnam. In 1991 he won a famous tank engagement against Saddam Hussein’s Republican Guard, the Battle of 73 Easting. After 9/11, he went back to Iraq and won a reputation as a military and political thinker open to diplomacy but unafraid of hard offensive action.

McMaster with Donald Trump at Mar-a-Lago in Palm Beach, Florida, on his appointment in February 2017. Photograph: Susan Walsh/AP

Thirty-eight years ago, however, McMaster was just another freshman – or plebe – at the United States Military Academy. He was recruited to play quarterback, although “when the coaching staff recruited me they didn’t pay too much attention to my height”. McMaster is a compact 5ft 9in, which meant that he “couldn’t even see over the offensive line”. Perhaps reasoning that Ulysses S Grant was an inch shorter and that never stopped him rising to the very top, McMaster followed the path of many West Point football players and made the switch to rugby.

As a wing who looked and played “like a flanker”, he had four seasons of hard training and hard socialising and the all-consuming quest to beat Navy. Sometimes he won and sometimes he didn’t and he met his wife, Katie, via a couple of parties during a tour of California. And then in his final year, against Navy in a game won with a last-minute try, his opposing number turned out to be a high-school football team-mate.

That’s now a good rugby story, of the kind told in bars the world over in English, Spanish, Serbo-Croat and Swahili, with gathering pace as a World Cup in Japan approaches. Like most players McMaster has many such tales, told with requisite laughter.

The West Point team, with McMaster kneeling fourth left on the front row, before facing Air Force in 1983. Photograph: Provided by Bill Jackman

He is for instance happily incredulous about his role in forming a club in Bamberg, Germany; about an Argentinian cavalry officer and fullback who enriched the team at Fort Knox in Kentucky; about watching the USA thrashed by Australia at Australian forces HQ in Afghanistan and letting diplomacy be the better part of valour. He’s even happy to remember “getting raked out and bleeding from the head or whatever”, prompting a perversely happy exchange about the days when rucking meant flashing studs slashing at any available extremity.

He only stopped playing, he says, “when I received no sympathy anymore from my wife when I was on the way to hospital”.

More formal, if equally bruising, is the long rugby relationship between West Point and the Royal Military Academy at Sandhurst. The Brits usually win but as McMaster remembers it, “We played them very close in my junior year over there and lost it with a bad call, a penalty kick, right at the end of the match, which is still seared into my memory.

“But here’s the thing. That was in 1983. And then years later I’m in Iraq, this is 2005. And we form this joint strategic investment team to rewrite the Iraq campaign plan. And a British officer, Brigadier Jim Richardson, is on that team with me. And we keep looking at each other, thinking, ‘God, we know each other. How do we know each other?’ And then Jim digs up a photo. He played centre in that match, in 1983. And I was playing wing. It’s just extraordinary that our paths would cross again, in Iraq, 22 years later.”

‘Bind together and overcome’

To McMaster, rugby and soldiering are two sides of a coin perpetually flipped by the Fates. “To win in rugby,” he says, “you have to be committed to each other and work together, play together as a team. And that’s what combat requires.

McMaster greets troops resting in an old maintenance building in Babil province, Iraq, in April 2005. Photograph: Getty Images

“It requires tough training under the most difficult and challenging conditions because it’s only that which builds confidence – confidence in your own skills, confidence in your team. That confidence in combat is what allows you to overcome fear, to take risk and to seize the initiative. It’s all about doing something unexpected, about exploiting what you create by rapid action and rapid decisions and operating together.

“A cavalry operation in combat in many ways resembles how a rugby team plays together.”

He continues: “You know what’s an amazing story? The eight man on our [West Point] rugby team, Harry Tunnell, was very seriously wounded in Iraq in 2003 or early 2004. And his leg required many, many surgeries. I think over 10 surgeries to save his leg. And the orthopaedic surgeon who did those surgeries was our scrum-half in junior year, Tim Kuklo. So the guy who was shepherding the ball out of the scrum to that scrum-half, now has that scrum-half save his leg.”

A cavalry operation in combat in many ways resembles how a rugby team plays together

He laughs again. “Unbelievable.”

Rugby also informs McMaster’s thoughts on combat and everyday life. On Veterans Day 2014, at Georgetown University, he delivered a now famous address about the “warrior ethos” and its place in the modern world. He revisits the theme.

“I think that these days there has been a tendency to regard soldiers as fragile and traumatised human beings,” he says. “And while it’s very important not to stigmatise combat stress and its negative effects, it’s also important to embrace a mild form of stoicism. To be able to overcome adversity.

“One of the key things we explain to soldiers prior to combat is, ‘You’re going to have a tough experience, sometimes harrowing, difficult, emotional – you’ll take away difficult memories. But it doesn’t have to screw you up. You can draw strength from your experience in combat with fellow soldiers. You can actually come out of it a stronger person.’”

Mcmaster, third left in second row, with other rugby players of the 1980s and coach Mike Mahan, front left. Photograph: Provided by Bill Jackman

From Play Rugby USA in New York to Memphis Inner-City Rugby in Tennessee, pioneering nonprofits are using rugby, in all its ugly glory, to build character among the deprived and neglected.

“I think the warrior ethos is analogous to what a good rugby team has,” McMaster says. “They’re not going to be daunted by another team, or a difficult a situation in a game. They’re going to bind together and overcome.”

Away from politics, soon to retire from the military, McMaster is in a supporting role himself. He’s enjoying NBC’s coverage of the English rugby Premiership; on CBS there is Major League Rugby, the new US professional competition. “That is some really good rugby,” he says. “I watched San Diego play Houston. It was a great match, came to the last minute, super high-scoring.”

He’ll watch Army and Navy again at the CRC sevens and he reminisces happily about Army’s 15-a-side win this year. And in doing so, he reaches for a suitably military phrase.

“Navy was driving, at the 82-minute mark, right at the death. But Army held the line.”