LAS VEGAS :McLaren's Formula One championship leader Lando Norris topped the Las Vegas Grand Prix timesheets on Thursday after second practice was twice red-flagged due to a loose drain cover. The track action was halted as a precautionary measure with 20 minutes to run after a marshal reported the problem just before Turn 17 of the floodlit street circuit. Red flags were then waved again with just over two minutes remaining to end the session shortly after the drivers had returned to the track