Stopping the clock

[eroombill]

I am a relatively new official. The rules, as I understand them, indicate that the clock should be stopped when the ball (and I assume runner with the ball) goes out of bounds. The more experienced officials tell me not to stop the clock if the runner is forced out of bounds or the tackler pushes him out. I cannot find a ruling to support what I am being told.

Any thoughts would be appreciated.