To make it tougher to knock the ball out of the end zone and curtail hang time on kickoffs, the NFL began using "K" balls. This NFL (Goodell) ball was used in Week 16 of the 2006 season. White end zone paint and surface blemishes vouch for use. Blue felt tip referee markings are apparent on the white lacing. "K" and WK-16" are engraved on the surface as well.