What rules govern touchdowns/touchbacks if there is a fumble involved?

Question

I have a question specifically about a passage of the official NFL 2018 rulebook (https://operations.nfl.com/media/3277/2018-nfl-rulebook_final-version.pdf).

Please take a look at Rule 3 - Section 2 - Article 7 (PLAYER POSSESSION)

My question is about the notes on page 5 of the rulebook. There it says the following:

(2) In the field of play, if a catch or interception has been completed, and the ball comes loose before the player is down by contact, it is a fumble, and the ball remains alive. It is also a fumble if the action occurs in the end zone of the player who caught the loose ball. If the action occurs in the opponent’s end zone, it is a touchdown or a touchback.

I don't really understand the last sentence of this Note:

If the action occurs in the opponent’s end zone, it is a touchdown or a touchback.

If I understood this rule correctly, the situation described is that of a ball coming loose after it has been previously caught or intercepted. Now: if I catch a pass in my opponent's end zone or if I intercept one of his passes in his end zone, I'm scoring a touchdown, no matter what happens after that. If I secure the catch and an opponent smacks into me, causing me to lose the ball, that's still a TD, since I controlled the ball previously. And if I fail to make the catch, that's an incomplete pass and the next play begins. So how could this situation (making a catch in my opponents end zone) lead to a touchback? What am I missing here?

Answer 1

So that only really applies to an interception or a fumble into the endzone, because the play is automatically over if an offensive player has possession of the ball in the endzone.

So, if you are a defensive player and intercept the ball or pick up a loose fumble and instead of kneeling down, you try to return the ball, but fumble in the endzone, the only results of the recovery can be are a touchdown, if recovered by the offense, or a touchback, if recovered by the defense or goes out of bounds through the endzone.