In the NFL, supposing a player catches the ball legally and runs with it, for a total of a 25 yard gain, but is hit to the head, causing a fumble before he makes contact with the ground (and is knocked out cold).
The opposing team lands on the loose ball and the refs whistle. I'm pretty sure the ruling would be the foul is assessed at the end of the run before losing the ball, thus the offensive team would have gained a total of 40 yards on that play.
However, the play was not dead at that spot (all other fouls would have nullified the play if the opposing team accepted the foul, so how can you nullify just half a play?). My question is, where would the ball be spotted and is there a reference that points to this scenario?