Rules of Safeties

Question
Help settle an argument!  Let's say the ball is on the 1-yard line.  The team tries to run a play out of the end zone, and the ball carrier is tackled.  Half of the ball is out of the end zone and half of the ball is one the goaline.  Is this a safety?  Is the rule of a safety that if any part of the ball is touching the line (based on where the ref rules the carrier to be down and the ball to be dead)or if ANY part of the ball is out of the goaline is is NOT a safety?  Thank you!

Answer
Paul, that's a safety, for two reasons: 1) The ball was on or behind the team's own goal line, and 2) the impetus came from a player on that team.

From the NFL Digest of Rules:
"The important factor in a safety is impetus. Two points are scored for the opposing team when the ball is dead on or behind a team's own goal line if the impetus came from a player on that team."