It appears based on his rear light he was on the brakes in that slight right hand turn. At first I thought maybe a tar snake but after the slow motion replay I can only guess maybe some loose gravel or something at the drive opening washed out the front.
Misapplication of the front brake in a turn. Most of your traction is used up in the turning process, doesn't take much to wash out the front tire when applying the front brake a little too much. I think he saw the rider in the oncoming lane, might have thought he was going to go wide and "grabbed" the front brake in a brief moment of panic. The oncoming rider was lucky. This is why you've got to be on your toes, I'm not concerned about my skills, it's the guy coming around the curve that scares me.
yeap
Front brake
See the twich in the rear before the fall
Most people that have ridden for a while always trail the back brake when braking
Probably why GP riders have rear brakes
Nah. It was the loose dirt and gravel from the driveway. Look at the dust that kicks up. He actually modified his line partway through the corner and went more inside thus increasing his lean angle. Watch his position in the lane. And yes he probably did it because of the oncoming bike.
That's gotta be it then, braking. I'm still a little baffled by it; he couldn't have been doing more than about 30 mph.
The guy in the white helmet directly in front of him took almost the same line through the curve and made it just fine; I didn't see his brake light come on. There does look like some dust and other loose sediment spilled over onto the road but it doesn't look THAT bad.
I think the crasher saw the decreasing radius... and maybe the oncoming rider... and hit the brakes at just the wrong spot. But again the road doesn't look terrible. Maybe worn tires was a factor; I can't tell if his rears have any tread on them at all.
Second thought, and not to take the fun out of the ride, but, they were all going to fast for the unknown conditions.
Clearly its an attack of that little road gremlin. The rider most likely doesn't have one of them bells attached to the front of the bike.
What else could it be..