Question about field goals...

[asmosley]

My friend and I are having this debate about what is legal if an attempted field goal is short. He claims that as long as the ball does not go out of the endzone on the fly, anybody on the opposing team can return it for a possible touchdown. My stance is that this is treated like a PAT...if the defender gets possession, then the play is whistled dead. What is the official rule on this? Thanks!