Sit Punches is a move used by the Jack series of androids, Prototype Jack and Kuma I since the first Tekken game, as well as Kuma II and Panda from Tekken 3 until Tekken 5. Ganryu can also perform this move in the arcade version of Tekken only.
In the first game, a forward motion is required to be inputted with each punch in order to move forward, otherwise the fighter will swing their arms in place without advancing. This feature was removed in subsequent games and the fighters will always move forward.