PHOENIX — NFL owners approved two rule changes Tuesday to enhance player safety. They might not vote on a proposal to ban offensive players from using the crown of their helmets against defenders. The owners outlawed peel-back blocks anywhere on the field; previously, they were illegal only inside the tackle box. A player makes a peel-back block when he is moving toward his goal line, approaches an opponent from behind or the side, and makes contact below the waist. The penalty will be 15 yards. Also banned is overloading a formation while attempting to block a field goal or extra …