No, it isn't fake. When I go biking downhill etc - and whilst I've never had something any where near as bad as this - I still find out almost daily that rocks and smaller stones become bullets when your wheel kicks them up. They create fairly large dents in metal, and there has been cases with me when I've had smaller stones go into my leg just from the kick up from the front tire.
This happened when a rider infront of him hit the stick and he rode into it. It had become propped up and it went straight through when he rode into it. The reason its got nicely cut ends is that ambulance crew had to cut the ends off to get him in apparently.
So to all that say "this is fake" etc etc; just because you weren't there to witness it, doesn't mean its not real... Freak things like this happen all the time in sports. A Skiier got decapatated by a small branch, a surfer lost his legs to a rock. Speed + obstacles = injury/death every time.
So don't dismiss it as fake... At least look up backstories before you make up snap judgements.

 WHAT THE FUCK MANNNNNNNNNNNNNNNNN

 WTFFF

 what a bitch tickiling branch hole

 Hehe, +2

 dident see that comin

 even though its faked, pretty bizare.

 +2

 not fake

 ahhh shit that is sick

 yeah f*cking sick man

 FAKE AND GAY!

 PHOTOSHOPPED