Holdbacks and bigger kids are always going to be there - you can't ban them from lacrosse and playing at their grade level. A better solution to even things out would be to give smaller kids the option to play back a grade level like they do in another contact sport -- football. That way a parent who is concerned about their childs safety has a choice of what level his kid plays at rather than being forced to play against bigger kids. It would be very easy to institute some weight guidelines for playbacks at each grade level.