When one of the rear wheel bearings went bad on my F250, it locked the rear wheel up tight. The tire skidded and I almost lost control. After I came to a stop, and assessed the situation, I put the truck in 4WL, and backed it up a little, and then forward, and then back until it freed up, and limped home at 10MPH.
The problem is called a cage failure. There is a soft metal cage that keeps the rollers from touching each other and creating great friction. The cage is supposed to float ahead of the rollers, and just be lightly pushed out of the way as the bearing turns. However, if you get dirt in the bearing, or the lubrication gets bad, a roller can catch hold of one of the bars in the cage and drag it into the bearing. That acts like a wedge that locks up the roller and races and will really stop a wheel fast... in some cases it can even twist the spindle right off of the vehicle.
It usually isn't enough to just replace the races and the bearing. Usually you need a new spindle too, as the race galls up the bottom of the spindle as it plays sleeve bearing.
-Chuck