After much deliberation, I submit that the correct result in this play is that it is a touchback
We are all trying to use force as a guideline for why this would be a safety. But we have all agreed that the rule specifically states the term force is used only in connection with the goal line
and in only one direction, i.e., from the field of play into the end zone. Initial force
results from a carry, fumble, kick, pass or snap
Since the definition of force cannot be applied for a ball going from the end zone into the field of play the fumble is NOT an initial force NOR is it a new force – by definition straight from the book
Since there is no new force by the fumble this play is the same as; B1 intercepts a pass in his end zone. He starts to run it out but fumbles. B2 attempts to catch the airborne fumble in the end zone where B3 falls on it. What do we have? Obviously a touchback
We are trying to use an intricate knowledge of the rules to make too much of a simple situation.
Intercepted in the end zone, fumbled and recovered in the end zone, 1st and ten on the 20 for “B”