The Patriots' trick play that got John Harbaugh mad

In the third quarter of Patriots-Ravens, New England ran some plays out of an interesting formation:

After the play, John Harbaugh ran onto the field to yell at the officials, drawing a penalty:

At first glance, nothing looks strange. The center is surrounded by two players on each side. But then the player two guys to his left -- the "left tackle" -- sprints upfield to catch the ball. Aren't offensive linemen not allowed to do that?

A closer look reveals what's happening:

A team is allowed seven players on the line of scrimmage, and of those seven, only the player on the end of the line of scrimmage is an eligible receiver. The rest are "covered," and therefore ineligible.

Shane Vereen, the circled player, is actually "covered" by the receiver below him, and therefore, he's ineligible. That's why he backs up a bit on his route: if he were to go downfield, they'd be flagged for ineligible man downfield. And the last player on the line of scrimmage on the other side of the field is Michael Hoomanawanui, the "left tackle" who ends up catching the ball.

Essentially, the Patriots were playing with four offensive linemen: The center, the traditional right guard and right tackle, and the left guard. Vereen is playing "right tackle" even though he's a running back lined up in the slot.

This is very confusing for the defense, because somebody from a position that normally doesn't sprint downfield is all of a sudden an eligible receiver. This is the exact same play Alabama ran in overtime to beat LSU, hitting a large lineman in stride:

There is, however, one key difference between what Alabama did and what the Patriots did. Alabama sent its regular five offensive linemen onto the field, plus an additional tight end who looked kinda like a lineman. Nothing about Alabama's personnel tipped off LSU to the fact a trick play was coming. Thus, the surprise when the "left tackle" takes off down field.

The Patriots do not keep their normal personnel. They send out only four offensive linemen, with six players normally considered eligible receivers, one of whom reports as ineligible. This ineligible player tells the ref, and the ref has to tell the defensive captain.

This tips off the Ravens to the fact that something is up, but it raises a different question. Of those six players who are normally eligible, which five are?  This is what befuddles John Harbaugh:

John Harbaugh is none too pleased about that third-quarter drive where the #Patriots used four linemen. pic.twitter.com/CSHNxHueTv

— Tim Whelan Jr. (@thattimwhelan) January 11, 2015

He's mad because the refs didn't give him time to diagnose the problem, and to be honest, he's out of luck. He's right that it is the referee's responsibility to announce if an ineligible player reports as eligible or if an eligible player reports as ineligible. That happened. Vereen told the ref he was ineligible.

However, it's not the referee's responsibility to allow the defense enough time after that announcement to figure out which five players are eligible. The Ravens had the information the rulebook allowed them. Their inability to identify who was available to catch a pass and who wasn't is their own problem.

Brady on complaints about 4 OL in game: "Maybe those guys gotta study the rule book and figure it out."

— Around The NFL (@AroundTheNFL) January 11, 2015

(Also, it's funny that an NFL coach said "nobody has ever seen that" when a major college team ran that play in a nationally televised game against another major college team about two months ago. Come on, John.)