By enforce it I meant along two lines. One how is USSF gonna monitor all the little individual leagues, who modify USSF rules all the time. Two, how is it gonna be illegal in a game. An Indirect Free Kick if you head the ball? What if it just hits a head (could end up like another "handball", "headball" chorus from the fans).
They can't enforce, just like most other sports have no real control over the youth game. But by making the 'recommendation' it has to have an effect on the way coaches, leagues, and parents respond - to allow heading of the ball is now an active decision to go against a governing bodies recommendation.
I would assume it would be handled in the same way as unintentional/intentional hand ball is handled, but should be much easier to determine. And i agree it is not just about head to ball, but the act of putting your head in danger's way for contact with another player's body or with a high boot.
I also found it interesting about limiting heading in practice as well for older kids. There seems to be a consensus around the idea of non-concussive but repeated lesser blows to the head being a very dangerous thing - and that is actually something more likely to happen in practice than in a game.
