At the Olympic Stadium: Team USA's men have dominated the medal podium in the 4x400 relay, but this time they'll be minus injured Jeremy Wariner, who ran the last leg to lead the U.S. to gold in Beijing, and LaShawn Merritt, who is also out with a hamstring injury. In the women's 4x100, Team USA's Allyson Felix, gold medalist in the 200, and Carmelita Jeter, silver medalist in the 100, face a challenge from Jamaica's talented and deep roster. In men's pole vault, Brad Walker qualified Wednesday for a chance at a medal. Morgan Uceny and Shannon Rowbury are the American medal hopefuls in the women's 1,500 meters.At North Greenwich Arena: In the men's basketball semifinals, Team USA faces familiar foe Argentina, which lost by 29 points to the Americans in the final game of pool play Monday. Adding to the drama, there's bad blood between the two after Argentina's Facunda Campazzo punched Carmelo Anthony in the groin -- said to be retaliation for Chris Paul punching Campazzo. In the other semifinal, Russia, a surprise winner in its group in the preliminary round, relies on size, depth and Minnesota Timberwolves forward Andre Kirilenko. For Spain, the Gasol brothers, Pau and Marc, are hoping to help their team to a gold medal rematch with the U.S., who beat the Spaniards in the final at Beijing. At ExCeL Exhibition Centre: In taekwondo, Sugar Land's Steven Lopez, a gold medalist in 2000 and 2004 and a bronze medalist in 2008, tries to keep the family's Olympic medal streak alive in the 80kg division. Sister Diana lost Thursday in her bid for a medal in the 57kg division. At Olympic Park: In BMX cycling, Alise Post carries the U.S. women's hopes after qualifying in the middle of the pack Wednesday. In the men's competition, 19-year-old Connor Fields, the world time-trial champion who was born in Plano, and David Herman are medal hopefuls for the Team USA, which won three medals in Beijing when the sport made its debut.