block kick
 

team K ,4th and 18 from its own 18 yard line. K1 is at his own 1 yard line when R2 blocks his punt. The ball deflects to K2, who is T HIS OWN 2 yard line. His momentum carries him into his own end zone ,where he falls to the ground.

Is this a Safety?

I can’t speak for NFHS, but in NCAA this is a safety. Momentum only applies to an opponent’s kick, pass, or fumble.