If Samu Manoa is anything to go by, when the decades-long wait for rugby union in America to take off comes to an end, the world had better watch out.

The Tongan-descended, Californian-born colossus has formed a partnership with England's Courtney Lawes in Northampton Saints' second row that is redefining the position – and making opposition fly-halves nervous.

"When we're both on the field, we tend to talk to each other," Manoa growls mischievously in an accent part Pacific islands, part Snoop Dogg. He mimes a sideways glance between him and Lawes, nicknamed the "bruise brothers" by Northampton's local newspaper.

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"We'll see who's going to get the biggest hit and we'll see who gets the most. We just kind of count it as we go along. One of us gets a good one and we look at each other and go 'hmm… that's one for me'."

Eddie O'Sullivan, the former Ireland and USA Eagles head coach, recently had a hand in a trials weekend for sportsmen deemed to have the skills to take up rugby. One day the big bang may happen but for now gridiron, baseball and basketball have a hundred years of cultural rooting in schools and in adult Americans' hearts and minds. Rugby is mostly a social game in small clubs promoted by ex-pats.

"I see a lot of football players who try it out and say 'it's not for me'," says Manoa, who was born in Concord in the east of the Bay area surrounding San Francisco, where he went to Mount Diablo High School and trained for rugby to keep fit in the football close season. "Those that have come out of NFL usually go to Sevens, if anywhere." Witness Carlin Isles, the USA Sevens player and reputedly the fastest man in rugby, who joined Glasgow last month – and has so far played only sevens.

Manoa is one of six nominees as the Aviva Premiership's Player of the Season, to be named on 15 May. He has stiff and cosmopolitan opposition from two all-English full-backs – Mike Brown and Chris Pennell – plus the face-tackling Namibian flanker Jacques Burger, Fijian finisher Niki Goneva and New Zealand back-row warrior Dan Braid. More pertinently to this story, Manoa is one of only seven USA Eagles who play in the Premiership – and only he and Saracens' Chris Wyles are regular starters, although Cam Dolan is tipped by Northampton to make a breakthrough with them next season.

"It's hard in the States to get everybody to train because the players are all over the country," says Manoa.

"There's a league for the west-coast teams and that's the highest level you'll get until people start putting in as much money as you see in Europe. They need to come to one mind and focus on one thing. Until then we're just going to be chasing. Right now we're just happy to have qualified for next year's World Cup."

Manoa's full first name is Samuela which is worth noting by writers and broadcasters who make the anagrammatic slip of calling him Manu Samoa. Viz the US TV commentators whose excited description of a typical tackle on Ireland's Peter O'Mahony last summer went something like: "Huge hit! Manu Samoa! Hello, hello! Talk about crash-test dummies… wow… 6 6 and 286 [feet and inches and pounds]. Some dental fillings are being loosened at this moment."

But Manoa offers much more than brute collisions. His handling, support play and athleticism in the set-piece are on the brilliant side of accomplished. And he can tell his own story entertainingly.

His Twitter account comes across as a homage to Nike and Beats by Dre, and is written in gangsta shorthand: "Playn Pro Rugby Inda U.K, Makin Mula 4 Me & Minez…" His upbringing is jarringly out of synch with Northampton's Franklin's Gardens where a chorus of "Oh When the Saints" is the supporters' idea of raucous.

"The gang culture was every- where around the Bay Area," says Manoa. "It was heavy. Every other day, on the news, somebody just dies, a drive-by shooting. My brother got stabbed a couple of times. But every city's got a ghetto, it doesn't mean it's not a good place to go. Everywhere in the Bay Area is beautiful – even in the ghetto, man, that's probably where you wanna go for the best food."

I've brought along a map of San Francisco for context, and Manoa points to where there is a large Polynesian and therefore rugby-disposed population: in Oakland, San Leandro, San Francisco, San Mateo, Menlo Park and EPA (East Palo Alto). "There are rugby clubs: San Mateo, the EPA Bulldogs and Razorbacks… And that's us right there in the middle – TI." That's Treasure Island, home to his old club, San Francisco Golden Gate. Turn west for Alcatraz and the world-famous bridge.

"If rugby hadn't worked out I'd still be an electrician or helping my dad with his concrete work," Manoa says, counting himself, his wife Lo and their three children – with another on the way next month – as blessed. And why wouldn't he? "Retaining walls: I used to hate building retaining walls. I'd be doing a lot of the diggin', haha. Foundations. Yeah, man. Over there it's a fast life. You gotta hustle on the side, do stuff you don't want to do to make ends meet. Here, man, it's a piece of cake, all you're doin' is playin' rugby."