San Francisco 49ers running back Xavier Omon (33) runs for a first down in the fourth quarter, chased by Oakland Raiders linebacker Darryl Blackstock (56) and defensive end Tommie Hill (78), as the San Francisco 49ers take on the Oakland Raiders in preseason action at Candlestick Park in San Francisco, Calif. on Saturday August 20, 2011. Photo: Michael Macor, The Chronicle
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