YFZ Motor locking up.

Ok so we was at the sand dunes last fall. 2008 YFZ450. Bike was running very healthy. Then one time I let my buddy take it for a spin and he had a hard time getting it started. (He was used to fuel injection). He finally got it started drove it maybe 200 yards and motor locked up. Got it to spin free again only to lock on me again after about 1/4 mile. Couldn’t get it to start again until I took the crank plug off and spun backwards very easily and then started again. I was thinking crank or rod bearings but Iv heard some people say it could be the one way starter bearing. Question with that is… if the one way bearing would lock up, would it actually lock the motor up or would it just spin the starter? I tend to think it would just spin the starter and fry the starter pretty quick but maybe I’m missing something ?