Stopping the clock?

[Spence]

Can someone tell me or post the wording that determines when an official stops the clock for a play that has the ball carrier/receiver end up out of bounds?

For example, receiver catches the ball on the sideline , gets his feet down, DB immediately knocks him OOB. Clock did not stop.

Receiver catches the ball and runs OOB. Clock stops.

Is it as simple as who caused the OOB to occur? If the defense knocks the player OOB it keeps going. If the runner runs OOB on his own volition its stopped?