Dean Karnazes -- a famous ultramarathon athlete -- was terrifyingly attacked by a coyote during a run on a California trail this month ... and the incident was so bad, it left him with a bloody face.
The 59-year-old went into detail about the encounter in an IG video ... saying he was running in Marin Headlands when a coyote ambushed him.
"I just had something rather terrifying happen," Karnazes said. "I'm out on a 150-mile trail run and I got attacked by a coyote."
"That's a first. It knocked me over and thankfully I'm running with poles so I whacked it and it ran away.