In week 15, the Lions played their last road game of the season out west against the Arizona Cardinals. After a scoreless first quarter, the Lions scored their only points of the first half with a 1-yard touchdown run by Mikel Leshoure. The Cardinals responded with 3 consecutive touchdowns: first, Beanie Wells scored a pair of rushing touchdowns from 5 and 1 yards out respectively, then Rashad Johnson intercepted a Matthew Stafford pass and ran it back 53 yards to put the Cardinals up 21-7 at halftime. Each team kicked a field goal in the third quarter: first the Cardinals' Jay Feely from 51 yards, then Detroit's Jason Hanson from 41 yards. Arizona capped their win with two touchdowns in the final quarter: first Greg Toler intercepted a Matthew Stafford pass in the end zone and ran 102 yards for a touchdown, then Beanie Wells scored his third touchdown of the game, this one from 31 yards out.. How many points did Arizona lead by at halftime?