Touchback/Safety penalty

[Welpe]

Force is not a factor here because it doesn't matter who put the ball in the endzone. Team B screwed up by committing a foul in the end zone and this foul is enforced under all but one. This foul is the "but one", which is a foul committed by the offense behind the basic spot. That foul is enforced from the spot of the foul. The spot of the foul in this play is Team B's own endzone and it will be enforced from the endzone, resulting in a safety. Force is not a factor in any of this.

This is the same as if Team B intercepts a pass in their own endzone, and the runner returns the ball to, for example, the B25 but a Team B player holds an A player in the endzone. This is also a foul by the offense behind the basic spot, so it is also enforced from the endzone and is a safety.