I like the assumption that coaches in the NFL don't teach their players this rule. Someone should probably send them a link to this thread to make sure.
Less sarcastically, let me explain the major flaw in this thread: There is no concept, whatsoever, of the physics or awareness of the cornerbacks and safeties doing so. As if not being taught is not the problem instead of the fact that it's extremely difficult to change the inertia of 200-250 lb body or the reality some CBs will be better at pushing a receiver out of bounds by by knowing where the marker is. Not to mention closing speed. There's a huge element of 'luck' in pushing a receiver out of bounds as well, given that they need to be close enough for the impact force to move them - which is easiest when the receiver is already in the air and headed towards the line. A 'stationary' target (a player jumping straight up in the air), or one moving away from the sideline, require a lot more force to change inertia. A little physics application would go a long way in this thread.
Furthermore, anyone who thinks Sherman just didn't know the rule, that he could have just shoved Demaryius Thomas put of bounds (not to mention the fact that if Sherman hit his legs, he would have toppled him forward rather than gone backwards (again, physics, especially torque)) is being unrealistic. Unless you think Sherm is going to catch a 230 pound human being, which you shouldn't, then maybe it's time to give due credence to the fact these are professional players with all the ability that implies. People should act like this is case.