SAN ANTONIO -- The Professional Bull Riders (PBR) have announced that the top 35 bull riders in the world will compete against the best bucking bulls on the planet when the PBR Built Ford Tough Series returns to the AT&T Center for the San Antonio Invitational Friday and Saturday, Aug. 17-18. Bull riding begins at 8 p.m. on Friday and at 7 p.m. on Saturday. . . .