NFL illegal touching, explained: What is 'reporting as eligible'?

The NFL's Week 17 iteration of Monday Night Football (that fell on Saturday night, before the Sunday games, yes, I'm as confused as you are as to what day of the week it is) lived up to the hype, until it didn't. The game was closely contested and down to the wire, but the spotlight would be on a controversial penalty called on a two-point conversion that the Detroit Lions completed that would have put them ahead of the Dallas Cowboys with less than a minute on the clock.

We detailed the full controversy of that specific play and penalty here.

The penalty was called illegal touching, and if you're confused about that term or what the penalty is, that's understandable. The penalty (which is actually fully named: Illegal touching of a forward pass) had been called just twice this season before the controversial Lions penalty, and it was called seven times all of last year.

Since the year 2000 season, it has been called a grand total of 152 times.

What is illegal touching?

In layman's terms, only a select group of players can normally legally touch the ball on a forward passing play, typically, that is players who are numbered 0-49 and 80-89 and on the ends of the lines.

Here it is a bit more technically, straight from the NFL's rulebook:

It is a foul for illegal touching if a forward pass (legal or illegal)
thrown from behind the line of scrimmage:

(a) is first touched intentionally or is caught by an originally ineligible offensive player. If such a pass is caught, it is a live ball; or
(b) first touches or is caught by an eligible offensive receiver who has gone out of bounds, either of his own volition or by being
legally forced out of bounds, and has re-established himself inbounds. If such a pass is caught, it is a live ball.

Here is who is eligible:

Offensive players who are legally at least one yard behind the line at the snap, provided they either have the numbers of eligible players (0–49 and 80–89) or have legally reported to play a position in the backfield;

What is 'reporting as eligible' in NFL?

If a player who is not, by default, an eligible player and the team wishes to use him as a receiving player, the player needs to "report" himself as eligible to the referee before the play starts. They need to verbally let the official know they wish to be recognized as eligible.

Then, the player is announced as eligible over the loudspeaker so the defense is aware the player is eligible to catch a forward pass. Oftentimes, this announcement is not heard on television broadcasts.

For the Lions controversy in Week 17, player No. 70 was reported as eligible over the loudspeaker, however, No. 70 (Dan Skipper) was incredulous and believed to have said he never said anything to the referee. The Lions believed No. 68 was to be the actually eligible receiver outside of the norm on the play.