USA Football is introducing another tool as part of its road map for how the sport is played, coached and taught on the youth level. It's called TackleBar football. It's part of the Football Development Model launched last year. TackleBar will be one of three limited contact categories and serve as a stepping stone between flag football and the full tackle game.   Players will wear a harness with two bars in the back, one on each side. A defender can employ the basics of tackling — head up and out of the way while wrapping up — but without making contact.