I once made a sharp turn on my quad that completely threw me off of it and flipped it. Hard.
I could see a little more speed causing it to flip many times. I was knocked out briefly and hurt like an SOB for weeks. I was unable to get up for so long I started worrying about not being able to go to work, losing my job, my savings wiped out by medical bills...
I could see something like that happening on a wet sandy beach causing him to be knocked out, the vehicle to be damaged, and the tide coming in and washing him out to sea... where a shark did what a shark do.
That or sharknado.