NEW YORK -- Major League Baseball and the players' union have banned rolling block slides to break up potential double plays, hoping to prevent a repeat of the takeout by the Los Angeles Dodgers' Chase Utley that broke a leg of New York Mets shortstop Ruben Tejada in last year's playoffs.Under the rules change announced Thursday, a runner must make a "bona fide slide," defined as making contact with the ground ahead of the base, being in position to reach the base with a hand or foot and to remain on it, and sliding within reach of the base without changing his path to initiate contact with a fielder.