What baseball rule stops the catcher from just playing in the field when no one is on base?

Everytime there is a passed ball when there is no one on base the catcher just gets a new ball from the ump. Is there a rule that someone has to catch the ball or be there or anything?

Submitted May 30, 2018 at 03:43PM by YourGFblewMe https://www.reddit.com/r/sports/comments/8ne4aw/what_baseball_rule_stops_the_catcher_from_just/?utm_source=ifttt