Ben Shelton, 21, has the fastest serve in HISTORY and will be the face of American tennis for a decade... but he dreamed of a VERY different career

Aged 12 Ben Shelton was like millions of other American teenagers: his only dream was to become an NFL quarterback. He loved baseball too. Tennis? Just an occasional whack around, a bit of mixed doubles with his parents and sister. He had never left the shores of the USA.

Just nine years later he is the planet's 14th best tennis player and one of his country's brightest hopes at next week's US Open. And that bullet arm which was honed from childhood to pitch fastballs and throw passes to wide receivers has been repurposed to deliver the deadliest serve in the world.

In a sport where six years old is considered relatively late to start for budding professionals, Shelton's story is not just an outlier – it is unheard of.

'I played lots of other sports growing up,' the 21-year-old tells Mail Sport. 'I played basketball, football, baseball, soccer, I played it all. The sport I really fell in love with was American football. I played until I was 12 and that's when I started to take tennis a bit more seriously - probably because my sister was having some success, she's a year and a half older and I wanted to follow in her footsteps.'

So NFL was the plan? '100%. First, college football. When you're a little kid and you have those things in school, what do you want to be when you grow up? Every year I wrote pro football player, pro football player, always.

Ben Shelton, at the age of just 21, has become one of America's top tennis hopes already

'That was the path I dreamed of and hoped to take but I'm happy with where I ended up!'

What makes his unorthodox journey to the heights of his – eventual – chosen sport the more surprising is that his father Bryan Shelton was a fine player in his own right, reaching the fourth round of Wimbledon in 1994 and peaking at world No55.

A casual observer might look at the Sheltons and intuit the same old story: tennis dad trains tennis kid from the cradle, catching the apple and shoving it right next to the tree.

'That definitely was not the case,' says Shelton. 'I think my dad was OK with me not playing tennis because he knows how hard the path is. He knows tennis is one of the more expensive sports to do and that was going to be coming out of his pocket!'

Shelton belatedly learned the game from his father, being part of the team at the University of Florida where Bryan was head coach. In June of last year, Bryan resigned his post to travel with Ben full time.

Shelton (right) poses with his family at his sister's graduation last December

Scott Perelman was assistant to Bryan at the University of Florida and helped to coach Ben since his interest in tennis was first piqued.

'I first met Benny when he was nine years old,' he tells Mail Sport. 'At that point he didn't want to have anything to do with tennis. He would have told you at that age: my dad was a tennis player; I'm not going that direction at all.

'His dad just wanted Benny to be happy and be involved in a sport where he had passion. And at an early age that passion was not tennis.'

At 6ft 4in Shelton is tall but not by the standards of the biggest servers in history. Yet at last year's US Open he sent down two 149mph missiles in the same game. When you filter out obvious speed gun errors or outliers, Shelton's serve is the fastest of all time.

So how does he do it? The key is those early years spent doing everything other than tennis.

Shelton is a big hope for the USA at next week's US Open, and faces Dominic Thiem first up

'Serving speed has a lot to do with technique rather than just strength,' says Shelton. 'Big strong guys sometimes serve huge but sometimes not.

'I learned a great throwing motion from a young age playing football and baseball - it always seemed like I was throwing some sort of ball and I think that has translated to my serving motion.'

As well as having the fastest serve in the world, Shelton also has the most varied. He can apply enormous amount of 'kick' – the spin applied by brushing up the back of the ball – which causes the serve to rear up off the court and bounce out of reach.

Perelman ascribes that aspect of Shelton's serve to his years learning to balance fastballs and curveballs as a baseball pitcher.

'What we've been talking to Ben about since he was in college, is to be a pitcher with your serve,' he says. 'Not just a fastball - vary the pace, vary the spin, vary the power, that's where the ultimate effectiveness comes in. And this is what separates him.'

The tennis star rattled Novak Djokovic with his 'dialed in' phone celebration last year

Shelton's game is far from just a serve, though. He is an explosive athlete with a rocket of a forehand, a steady backhand and a rounded all-court game. From a purely tennis point of view there is something of the Nick Kyrgios about him. The talent of Kyrgios with, as Perelman puts it, 'a strong desire to excel and an off-the-charts work ethic' – that is a lethal combination.

And there is so much more to come, given this is only his second year on tour and ninth even playing the sport.

Perelman is in no doubt about Shelton's potential, saying: 'I remember vividly telling Bryan that coaching Ben in a match situation is like riding the horse Secretariat (the legendary, Triple crown Winning American thoroughbred).

'This is rare air in tennis – guys who are the total package like Ben is. He has all the intangibles to be the best player in the world.'

Off the court, he has plenty of endorsements and is hot property on the ATP Tour

Because of his belated interest in tennis, Shelton never travelled the world on the junior circuit.

'My upbringing was a lot different to other tennis players,' he says. 'I was at home all the time. I went to a normal school, I played the US circuit of junior tournaments which only happened at the weekends so I wasn't playing week-long tournaments in different countries. I never even left the country until last year (for the Australian Open).

'A lot of people think you have to travel the world and become a top junior to make it on the pro tour but for me it was a different path. I was on a different timeline to everyone else but I ended up in the same place.'

An upbringing outside the hot-house of junior tennis has made Shelton an open and engaging companion, with his toothy, megawatt smile never far away. He has also carried the strut of the high-school quarterback on to the court. His 'dialled in' celebration at last year's US Open - he mimed hanging up a phone - wound up Novak Djokovic to the extent that he mimicked it after beating Shelton in the semi-finals.

Shelton makes a return at the net during his match against Jannik Sinner at Wimbledon

That celebration brought allegations of arrogance but Perelman is firm on that point: 'He's confident but he's not arrogant,' he insists. 'This guy is special, one of a kind. He can walk into a room and light the room up.'

With the end of the Big Three era nigh and many of the current top players shunning rather than embracing the spotlight, Shelton is the kind of character desperately tennis needs.

'He loves that limelight and wants to do something special with it,' says Perelman with avuncular pride. 'He wants to bring young kids into the game, he wants to help society in any way he can. You ask young kids now do you know who Ben Shelton is and the place is going to jump up and down.

'Benny and Coco Gauff, they could be the face of American tennis for the next 10 years.'