You wouldn't DoS a car

from here and here (image source)

Sometimes whether a thing is an attack or a defense depends entirely on perspective. The motorcyclist could be trying to prevent his motorcycle from getting stolen, but the car owner can't go anywhere now because the motorcycle is anchoring him in place. You could make a lot of arguments about the motorcyclist knowing better, but this site has seen cars chained up as if they were bicycles, so I don't doubt this could have been a sincere attempt to prevent theft (even if it is ridiculous).