Hurdling is an attempt by a player to jump (hurdle) with one or both feet or knees foremost over an opponent who is contacting the ground with no part of his body except one or both feet. So if it is a lineman with his hand on the ground, it does not meet the definition of hurdling. If it is the center that gets jumped (hurdling), it would be a foul for hurdling if he has his hands on the ball. If the lineman, including the center has removed his hand from the ground when the jumping happens, then it would be hurdling. Timing of the act matters.