Touching the ball to the ground.

[Warrenkicker]

The ball being part of your hand in another of these old sayings which keep being told but aren't true. Playing until the whistle sounds can still get you a dead ball foul because the ball becomes dead before the whistle. The ground can cause a fumble when the player wasn't down prior to the fumble. A ball in a players hand is nothing more than that. Touching a ball to the ground is nothing more than just that. The ball isn't your knee, your shoulder, or your head. Were those to touch the ground while the ball was in your possession then you are down.

These sayings were invented by someone who liked to make generalizations. But whenever you make a generalization there is some specific instance that makes it untrue.