Sports briefs

Iowa starting defensive end Adrian Clayborn has been charged with punching a cab driver who honked at him in Iowa City.

Police say Clayborn left his vehicle, reached inside the taxi window and punched the driver before a friend pulled him away at about 2 a.m. on Jan. 18. The police complaint said the cabbie sustained minor injuries.

Two months later, the 20-year-old Clayborn was charged with assault causing bodily injury, a serious misdemeanor. He turned himself in to police Friday morning. Iowa's athletic department said he pleaded not guilty.

"I've been aware of this alleged incident since January and consider it to be a serious situation," coach Kirk Ferentz.

Klitschko title on the line Heavyweight champion Vitali Klitschko hopes to impress the lucrative American market when he defends his WBC title against Cuban defector Juan Carlos Gomez today in Germany. Toward that end, he'll pound on a good friend, live on ESPN.

Gomez is a frequent sparring partner, but putting on a show for U.S. viewers is more important than friendship.

"I like Juan a lot. He's a real nice guy and a good buddy of mine," Klitschko said. "It's a real pity that I now have to beat him up."

Chambers, who won the European 60-meter indoor title earlier this month, has published an autobiography, in which he provides details from years of systematic doping that left him a "walking junkie."

"The question is how to stop him from running," said Nick Davies, spokesman for the International Association of Athletics Federations. Davies said he wants to see whether Chambers can be excluded for "bringing the sport into disrepute."

Roddick, Nadal reach semifinals Andy Roddick beat defending champion and third seed Novak Djokovic 6-3, 6-2 and reached the semifinals of the BNP Paribas Open in Indian Wells, Calif.

Djokovic made 30 unforced errors, 18 more than his seventh-seeded Roddick.

Off to a career-best 23-3 start this season, Roddick next faces No. 1 Rafael Nadal ,a 6-2, 6-4 winner over No. 6 Juan Martin del Potro. No. 2 Roger Federer faces No. 4 Andy Murray in the other semifinal.

Maria Sharapova has withdrawn from the upcoming Sony Ericsson Open in Key Biscayne, Fla., saying she's not ready to play a full tournament as she recovers from a shoulder injury.

New test to be ready for '12 Games A German lab has developed a new test for gene doping that should be ready for use at the 2012 London Olympics.

Gene doping, the practice of using genetic engineering to artificially enhance athletic performance, is believed by many to be the next frontier in drug cheating.

"The test is ready to be used. For sure we could go ahead with testing for gene doping at the 2012 Olympics in London and probably a lot sooner," said Mario Thevis, a researcher who helped developed the test.

The test awaits the approval of the World Anti-Doping Agency.

Soccer: Portland will join Major League Soccer in 2011, expanding the league to 18 teams. Vancouver was added to the league earlier this week.