[whistleblowerusa]

I would like to add my 2 cents. Greyhound is correct, not only because the advise book says so but because the Laws also describe what is fair or not. Anything that is considered reckless, careless, or using excessive force must be penalized. Making contact with the ball first is one of those many soccer myths of the game. If a defender takes an attacker down while tackling the ball away and has no way to avoid making contact with the attacker and is placing himself as well as the attacker in jeapordy, then he/she must be sanctioned.
The referee must be sole judge of players of different sixes trying to play the ball fairly. He/she must be careful not to take away a players advantage in play simply because of size. If play is fair then obviously no foul.
If a player steps infront of another player as described in your last situation, it isn't impeding the progress of an opponent, although it may appear that way. You can only impede a player by placing yourself between him/her and the ball. Since in the situation you describe, the player steps infront of the attacker to knock him off the ball, it should be considered as charging or pushing and the restart should be a direct free kick. Even if there was impeding the progress, once there is contact made by the defender, then it is no longer impeding and not an indirect free kick, it is holding or pushing or charging and must be a direct free kick.