This week we'll be detailing the rule changes for the 2010 NFL season. The rest of the series can be found here.
Starting this year, a play will be blown dead as soon as the runner's helmet comes off during the play. This only applies to player with the ball. As soon as the helmet comes off, the play is dead and the ball is spotted where the helmet came off. It will be treated as if the player was down by contact.
For example, this play by Jason Witten against the Eagles would have been blown dead at the 35 yard line.