It was what the free runners call a 'bail and slam”.

It means as it sounds – a failure, a painful failure where an airborne body collides with an immoveable stationary object.

In this case it was Dan Mills' head – he did a backflip into a wall, cracked his head, stood up and collapsed. He was comatose as his mother drove to hospital.

'Also tore the ACL in my left knee.”

Dan's mum didn't much care for freerunning in those days. But she has come round.

His sidekick, Tyler Lloyd, has single-handedly put a dent in the national health budget. 'Fractured ribs, contusions on my lungs, broke this bone, broke that bone, tore muscles in there and a big screw in my wrist.”

This is perhaps scare-mongering and an unfair commentary on freerunning – something Dan and Tyler and a small community of local adherents, half a dozen of them, regard as a legitimate sport, an artform, free form gymnastics in the street.

And to be fair, motocross, base jumping, skateboarding and rugby can all be dangerous too, even deadly. Case in point – just this week Black Cap Mitchell McClenaghan fractured an eye socket after a bouncer ripped into his helmet. And his head.

To know is to understand, so what's freerunning?

It's like Parkour, a military discipline to get from A to B smoothly and efficiently as possible and involving running, climbing , swinging, vaulting, jumping, rolling. Movement covers it.

'Yeah, freerunners do all that too,” says Tyler. 'But we do it with gymnastics and as flashy and showy as possible. Yeah, we show off.”

Freerunning, as the name suggests, is a little more organic than parkour. It's an acrobatic and athletic discipline.

'Depends on where we are. If there are some ledges we would be running and launching over them.” Yes, airborne bodies, bodies in free flight. 'Flipping and tumbling and the like. Out of control gymnastics.”

And what is a freerunner? Probably someone with a martial arts background, such as Tyler, who was seeking a more adrenalin-pumping sport.

For that reason they will love the daredevil, the indiscipline, the recklessness, the spontaneity. But they remain serious disciplined athletes.

They have been refining their craft for 10 years and talk of it in formal terms even though it's unstructured. There are no manuals, no coaches, no rules.

'We train most nights for a couple of hours after work.” Leaping on things, off things, over and around things. 'And six or seven hours a day at weekends. I can't walk by the end of the day. And I was still sore Monday.”

Freerunners talk a lot about being in tune with their bodies. These are young, taut and tuned bodies and they are delightfully aware of themselves. And eminently likeable to boot.

'Knowing what our bodies are capable of,” says Dan. 'Knowing what muscle does what, maximising them, driving ourselves to the limit. Understanding and controlling ourselves.”

All seems a bit abstract, a bit ethereal, but it seems people free run for two reasons.

Of course there's the personal satisfaction. 'The movement and the expression,” says Tyler.

'Yeah, we love it and crave it” says Dan. 'But shooting videos is a huge part of it – everyone is up on YouTube showing off.” There's ego in every sportsman, they all need to be seen, to win, and crave adulation.

Yes, they have done what many would consider the dumb stuff. They clambered up on the Matapihi rail bridge. Luckily no trains, no injuries, no damage that day despite one of the free runners doing a backflip up there. That's in the distant dark past and not worth re-litigating.

But people will catch them 'doing crazy stuff” up on buildings. 'And they'll freak out,” says Tyler.

'We have been standing up there for half an hour, but we aren't frightened. We are contemplating and planning and sizing the jump. We even size it out down below to make sure it safe and achievable.”

'For us it's more a calculation thing and when we get the calculation right and we finish the trick and it works out… well, that's why we do free running.”

Dan and Tyler are seeking respectability and acceptance for their sport.

'When skateboarders were something called street surfers, looking for a real name and acceptance, it took ages. But it happened.”

It'll come guys. One day.