A sometimes controversial rule is usually referred to as "the ground cannot cause a fumble". If a player is tackled and loses control of the ball at or after the time he makes contact with the ground, the player is treated as down and the ball is not in play. However, in the NFL and CFL, if a ball carrier falls without an opponent contacting him, the ground can indeed cause a fumble. This is because in those leagues the ball carrier is not "down" unless an opponent first makes contact, or the runner is out of bounds. If a player fumbles in most other leagues, as soon as the knee or elbow touch the ground, the ball carrier is considered down. It is also possible for the ground to cause a fumble in college football if the ball hits the ground before any part of the ball carrier's body (other than the hand or foot) touches the ground. An example was the fumble by Arkansas quarterback Clint Stoerner vs. Tennessee in 1998.
The one in his sig pic is the Desean Jackson college one and it was also ruled a fumble.