What is the call when a batter who just walked picks up the loose ball with runners on base?

Assuming the catcher is near home plate, the runner has to slide. If he doesn't and knocks the catcher down he is out. If the catcher is up the baseline and is waiting to make the tag the runner would be called out for crashing into him. If the slide knocks the catcher down, the outcome of the play would depend on whether the catcher maintained control of the ball during the tag and whether the runner touched home plate.