[don't move]

Page 74 of the case book Play 9.7.2 situation B (part a) is right on point. This is a punt batted by K into the endzone. Ruling: R may take the ball at the spot of first touching, they can accept the result of the play which is a touchback, or they can have K rekick after a 15 yd penalty from the previous spot.

Using the 20 yardline as the basic spot is not an option. It's a loose ball, previous spot foul, even though the final result of the play is a touchback.