Its an obscure rule and one I've never had to enforce. You'll find it in the "Pitching" section of the rule book, where it lists all of the responsibilities of the catcher (must be in the catcher's box, etc.).
The rule says that the catcher must return the ball directly to the pitcher following a pitch, except after a strikeout or on a put out attempt. The rule does not apply when there are runners on base or when the batter has become a batter-runner. The intent of the rule is to prevent a delay of the game. The penalty for violating this rule is a ball to the batter.
But wait...there's more!
The rules also say that to intentionally walk a batter the pitcher must throw four legal pitches. You can't walk a batter by willfully violating the rules, like by committing illegal pitches or by rolling the ball to the plate. So the umpire should not allow a walk based on a purposeful violation of the rules.
The first time a team tries this the umpire can choose to not award the ball to the batter. If they try it a second time it can be judged as unsportsmanlike conduct and result in ejection of the catcher.
My advice would be to not try this during your games!
