[Jim S]

The same rule, 2-28-2, says that a ball in player possession is OB when the runner touches anything , other than a player or game official, who is on or outside a sideline or endline.
A player is in the same clasification here as a game official.
Second if the player was a different situation it would still not be Illegal Participation since the play would be over because the ball would have gone OB.