Some context for those who aren't familiar with Australia and our fauna.
It seems the guys making the video were out pig-hunting. The dogs are "pig-dogs" - bred and trained to hunt feral wild boar (which are a pest in rural/outback Australia, they destroy fertile land and crops, competing with farm animals for space and food etc). It's not what I'd call a sport (I don't mind sensible culling, killing with dogs and often knives as "sport" is barbaric in my opinion, but that's just me), and the wild pig meat IS often eaten (so it's not hunting for the sake of hunting), so I can live with it. Boar can grow quite nasty tusks (modified canine teeth, basically) and dogs are often used to run them down and tire them out for a hunter to come in with a knife to finish them off.
Kangaroos are an interesting animal. Yes, they're on our coat of arms (Australia is the only country I'm aware of that eats the animals on its coat of arms). There are several breeds, this one's big but a long way from the biggest I've seen - some of the really big reds can stand well over 2m tall and weigh over 90kgs (6'6" and 200lbs for those who are metric-challenged). The males can be particularly territorial, and they're well equipped for fighting - those front legs aren't nearly as weak as they look (they're no T-Rex here), and the rear legs come with really long claws that can disembowel animals - male roos tend to have very thick and strong stomach skin to protect themselves from this. They are at times a protected species, at other times can be hunted and culled due to over-population. They're very adaptable, and between the red and grey kangaroos, are found across most Australian landscapes except for deep residential and cities. They can be very tame even as wild animals - but they can, as I said, be territorial and aggressive, particularly around breeding season.
The concept of the "boxing kangaroo" comes from their way of fighting - initially, they'll lean back on their tails (very muscular and powerful) and wave their front legs at each other almost like they're boxing - but it's a ploy to catch their opponent off-guard and grapple an opponent into a vulnerable position, at which point they lean right back on their tail and lash out with their hind legs. You can see the 'roo trying to do that to the dog in the video. Had it successfully connected, I've no doubt that the dog would have been gutted (literally) and died.
What the guy does is both incredibly brave (we all know people will at times do crazy things to protect pets) and stupid - unlike Kangaroos, people have soft fleshy stomachs. He lands what I'd consider to be a lucky punch to the roo's head and appears to stun it - he then makes a smart move and backs off before it can recover. I've no doubt that the roo could have inflicted a serious injury on the guy.
I dislike the video (I certainly don't find it funny - no funnier than a Texan finds "steers and queers" jokes made at their expense, I am sure). The commentary in particular seems very "put on" and faked, made to sound more "ocker" and stereotypically "outback Australian" than is legitimate (though there ARE some places where people do sound like this, the voices in the video don't have as pronounced an accent) - it sounds like a piss-take of Steve Irwin (he deserves better and more respect). I suspect the people in the video probably put themselves in a position for something like this to be more likely, but I don't think they "got out of it" terribly badly, and frankly, nor did the 'roo.
I'm happy to see mature discussion around it (and yes, what I don't find funny, others may, so I'm sure there'll be some jokes, but please, try to be respectful). If things deteriorate, I suspect you'll see the thread either locked or deleted - how people behave from here on will determine the path we tread I suspect.