Anyone want to play with the legal jargon that is considered the NFL Rule Book? Let's take a gander at the rulebook to see why the refs got it wrong and why it should have been a safety.
Here's the play in question:
Follow along (rule book here for your reference)! I've removed words that aren't relevant (like with regards to passing plays).
First, let's look at the definition of a safety:
Rule 3, Section 29, SAFETY (a)
A safety is the situation in which the ball is dead on or behind a team’s own goal line provided:
(a) the impetus (3-15-3) came from a player of that team;
MOMENTUM Note: It is not a safety if a defensive player in the field of play intercepts a pass; catches or recovers a fumble, backward pass, scrimmage kick, free kick, or fair catch kick and his original momentum carries him into his end zone where the ball is declared dead in his team’s possession. Instead the ball belongs to the defensive team at the spot where the ball was intercepted, caught or recovered. (11-5-1 Exc. 2)
So from here, we see that a safety is when the ball is dead behind a team's own goal line, provided that the team with the ball is the reason (key word: impetus) for the ball being behind said goal line. Of course, they had a subnote with regards to momentum, which means that if a player were to be running backwards to return a kick (ie: they were waaaaay too far up the field and had to run back to the goal line), and they caught the ball at the one, but carried themselves into the end zone, that would be a legitimate touchback.
We also see reference to two different sections: 11-5-1 Exc. 2 and 3-15-3. It should be noted that 3-15 is in reference to "Huddle" and there is no 3-15-3, so the entire rulebook should actually refer to 3-16-3 (Impetus!).
First, let's look at 11-5-1:
Rule 11, Section 5, Article 1: SAFETY
It is a Safety: (b) when an impetus by a team sends the ball behind its own goal line, and the ball is dead in the end zone in its possession or the ball is out of bounds behind the goal line.
Exceptions: It is not a safety: (2) If a defensive player, in the field of play, intercepts a pass or catches or recovers a fumble, backward pass, scrimmage kick, free kick, or fair catch kick, and his original momentum carries him into his end zone where the ball is declared dead in his team’s possession. The ball belongs to the defensive team at the spot where the player’s foot or other body part touched the ground to establish possession.
Exc 2 (exception 2) states that with respect to momentum, the ball belongs to the returning team where the player touched the ground to establish possession. For the sake of this return, it's clear that they never had possession until they were in the end zone. So the momentum theory goes out the window.
Now let's look at the definition of a touchback:
Rule 11, Section 6, Article 2: TOUCHBACK
When a team provides the impetus (3-16-3) that sends a loose ball behind its opponent’s goal line, it is a touchback: (a) if the ball is dead in the opponent’s possession in its end zone;
Note 2: The impetus is not from a kick if a muff, bat, juggle, or illegal kick of any kicked ball (by a player of either team) creates a new momentum which sends it on, above, or behind the goal line. See 3-16-3-Note
By definition, if the momentum of the kick is impetus that brought the ball into the end zone, then it should be declared a touchback. So let's finally look at the dang definition for impetus:
Rule 3, Section 16, Article 3: Impetus
Impetus is the action of a player that gives momentum to the ball and sends it in touch. The Impetus is attributed to the offense except when the ball is sent in touch through a new momentum when the defense muffs a ball which is at rest, or nearly at rest, or illegally bats:
(a) a kick or fumble;
Note 2: Momentum is not applicable (11-5-1-Exc. 2).
Rule 3, Section 2, Article 5: MUFF
Article 5 A Muff is the touching of a loose ball by a player in an unsuccessful attempt to obtain possession of it.
Emphasis my own.
The impetus is the action of a player that gives momentum to the ball. The ruling on the field implies that the kick is what sent the ball into the end zone, to be covered for a touchback. The definition of impetus states that a ball nearly at rest is no longer under the impetus of the kicking team should the returning team muff the ball.
Also, original momentum doesn't count with the definition of Impetus, where there is a new momentum by way of a muffed return.
Let's see the GIF again:
That's nearly at rest. That's a new momentum directed by the returning team. This should have been called a safety.
11-6-2-nt2: Impetus is not from kick if muff or kicked ball creates new momentum which sends it behind the goal line— Rich Hill (@PP_Rich_Hill) November 18, 2014