NFL rules questions

[tmagan]

If, on a field goal/extra point, while the holder is holding the tip of the ball (waiting for the place kicker to kick it), if he is touched by a defender, is the holder down by contact?

When a running back runs into the line of scrimmage near the hash marks, the umpire will not take that ball out of play, however, if the running back is taken down near the out of bounds line, the umpire will ask for a new ball for the next down. What is the criteria in terms of when the umpire should take the ball out of play on a running play?