Obscure rule led to Graham Glasgow playing left tackle for the Lions on Sunday

Amid a run of injuries during Sunday's game against the Indianapolis Colts, Detroit Lions left tackle Taylor Decker left the game with knee and ankle injuries after getting rolled up on from behind when Jared Goff was sacked. He was able to come back into the game after missing a series, but the play after he exited was odd.

Left guard Graham Glasgow moved out to left tackle, and Michael Niese came in to play left guard. After the play, Dan Skipper came in to play left tackle and Glasgow moved back inside to his normal spot.

Glasgow is very versatile, but without full confirmation that surely had to be his first career snap at tackle. The play-call can reduce, if not eliminate the risk of having Glasgow playing left tackle for a snap, and in this case Ben Johnson called a quick screen to Jahmyr Gibbs.

But why did it happen?

Justin Rogers of Detroit Football Network asked Glasgow about the lineup shuffling in the locker room after the game.

An obscure NFL rule led to Graham Glasgow playing left tackle

"Skip reported as eligible the play before, so you can't come in the next snap as an ineligible player unless you call a timeout,” Glasgow said. “I don't even know what was happening. They were just yelling on the sidelines and they just said, Play left tackle for a play.'”

Someone on the Lions' sideline was aware of the rule about being an eligible receiver on one snap and not being able to be an ineligible player on the next snap without certain circumstances happening.

Here's what Rule 5, Section 3, Article 2 says about when a player changes his eligibility from eligible to ineligible.

"ARTICLE 2. RETURNING TO ORIGINAL POSITION. A player who has reported a change in his eligibility status to the Referee is permitted to return to a position indicated by the eligibility status of his number after:"

"(a) a team time out;
(b) the end of a quarter;
(c) the two-minute warning;
(d) a foul;
(e) a replay review;
(f) a touchdown;
(g) a kick from scrimmage;
(h) a change of possession; or
(i) the player has been withdrawn for one legal snap."

"Penalty: For a player failing to notify the Referee of a change in his status when required, or an offensive player with an eligible number reports as ineligible and lines up outside normal five-player core: Loss of five yards for illegal substitution."

Notable there, as Jeremy Reisman of Pride of Detroit noted, is an injury/injury timeout is not on the list under the rule, which could impact a team's ability to substitute the player they want for an injured player. Going further into that, someone on the Lions' sideline also knew that an injury was not on the list of things that would've allowed Skipper to step in at left tackle without having to miss a snap.

It ultimately was not a big deal that Glasgow had to move over to left tackle for a play, and it appears Decker avoided a significant injury heading into a short week. But attention to the small details of an obscure rule led to the Lions not having to burn a timeout, or take a penalty, right after Decker left the game.