I don't remember the rule change, but if the B player fumbles the ball and it leaves the end zone and then returns, the fumble is now the new impetus making B responsible. If it goes out of bounds at the 1 though it comes back to the spot of the fumble (forward fumble out of bounds) and results in a touchback.
It wasn't so much a rule change, as editorial in nature. Adams had interpreted the rule to, essentially, say that impetus could not be changed IN THE END ZONE. There was an AR that was this exact scenario that made it 100% clear that the ruling for this scenario was to be a touchback. Thus, a fumble by Team B after a COP in the end zone would not change the impetus from the original loose ball (kick/pass/fumble, which would have had to occur in the field of play). Adams corresponded with me that it didn't matter if the loose ball from B's fumble happened to travel into the field of play, and then back again - the impetus was still from A's (pass/kick/fumble), as long as nothing changed the impetus while it was in the field of play. So, if it subsequently went OB behind the GL, it would still be a touchback. And, there was rule language that specifically told us that neither batting nor kicking (both illegal) in the end zone would change the original impetus, either. So, everything was covered. Impetus could not be changed by some action with, or on, the ball in the end zone. Period. Simple. Nobody got any unfair advantage by having it this way, and Team A couldn't get a cheap safety, just because B fumbled the ball, and it just happened to bounce back-and-forth across the goal line. Impetus was a defined action (i.e., carry, fumble, pass, kick, bat) with/on the ball IN THE FIELD OF PLAY that forced the ball into an end zone.
But, obviously, Redding didn't see it that way. This was nothing the Rules Committee initiated. And I am not aware of any game situation that may have happened that would have prompted him to make this change. He eliminated the language regarding batting and kicking in the end zone not changing impetus. So, now, they can. He eliminated former AR 8-7-2-III , which was the only direct ruling that, when a B player who caught a kick or intercepted a pass in B's end zone then fumbles the ball while still in the end zone, and the ball goes out of bounds in the end zone (directly, or otherwise, with no change of impetus), that's a touchback. But, strict reading of the actual rules, today, would require this to be a safety.
And I didn't 'skip' anything. The second part of that same sentence covers a ball that becomes loose in the end zone: ",...or is responsible for a loose ball being on, above or behind the goal line." When the defending team fumbles in the end zone, they are now responsible for this loose ball being out of bounds behind on/above/behind the goal line. It makes no reference as to where the impetus is imparted on the ball. If the ball is loose, the last team in possession, or the team that passed/kicked/batted the ball, is responsible for the ball being loose in the end zone. Period. So, if that impetus was actually made in the end zone, then that team is responsible if the ball then goes OB, or otherwise becomes dead on/above/behind the goal line. It makes no distinction as to the ball remaining in the end zone, or (while loose) traveling into the field of play, and then back again. The impetus from whatever originally put the ball into the end zone from the field of play is now expended. Impetus is now with the team that imparted the force on the ball while it was in the end zone. If that is the defending team, and the ball goes directly OB behind the goal line, by this rule (without previous AR 8-7-2-III that Redding deleted), that's a safety.
Now, no one wants a fumble by a B player in his end zone that goes directly OB to be a safety. And, I don't think anyone would, foolishly, rule that way. But, my point is, the rule language does not support a touchback in that case. If the Rules Committee really want to allow a fumble (or backward pass) by B after a COP in B's end zone that doesn't cross back into the field play and becomes dead in B's possession on/above/behind B's goal line to be ruled a touchback (and they should), and they really want a fumble (or backward pass) by B after a COP in B's end zone, that travels into the field of play and then back across the goal line where it becomes dead in B's possession on/above/behind B's goal line to be ruled a safety (I don't think they should, but, if that's what they want, OK), then they need to edit the rule, something like:
"The team responsible for the ball being out of bounds behind a goal line or being dead in the possession of a player on, above, or behind a goal line is the team that whose player carries the ball or imparts an impetus to it
from the field of play that caused it to be on, above or across the goal line when declared dead.
When, following a change of team possession in the end zone,
a subsequent loose ball travels into the field of play and the impetus remains unchanged prior to the ball becoming dead, the team responsible for the ball being dead behind the goal line is the team to whom impetus is charged to the loose ball in the end zone.
When, following a change of team possession in the end zone,
and the ball becomes dead without leaving the end zone, the team responsible for the ball being dead behind the goal line is the team that imparts an impetus to it from the field of play that causes it to be on, above or across the goal line when declared dead."