The New England Patriots used just four offensive lineman during a series of three plays in the third quarter of their 35-31 comeback win over the Baltimore Ravens on Saturday night.

It totally confused the Ravens and was so unexpected that the NBC announcers didn't even catch it during the live broadcast.

An explanation:

Under NFL rules the offense effectively has to have five players on the line of scrimmage who are ineligible to catch a pass. Normally, these five players are the offensive linemen, and they're stacked together in the middle of the field.

The Patriots didn't do that on those three plays. They used four clearly identifiable offensive linemen and had another player who was lined up in a different part of the formation declare himself as the fifth ineligible player.

The problem: The Ravens didn't know who that ineligible player would be until the referee announced it a few seconds before the play started. The Patriots were basically playing hide-and-seek with which receivers were eligible and which were linemen disguised as receivers.

After the game, Ravens coach John Harbaugh objected to the tactic, saying, "It was clearly deception."

Bill Belichick got to the heart of that deception when he said, "We had six eligible receivers on the field, but only five were eligible."

The Patriots scored a touchdown on the drive in which they used the four-linemen formation, and went on to win.

Here's a quick breakdown of how this worked:

1. Before the play, running back Shane Vereen declared himself ineligible to the referee. The referee announced it over the public-address system a few seconds before the snap. Vereen then lined up in the slot at the bottom of the screen, where you would typically find a wide receiver.

2. On the same play, the player lined up in the traditional left-tackle position, Michael Hoomanawanui, was actually an eligible receiver. He is the guy who eventually caught the ball:

3. When the ball is snapped, Hoomanawanui just leaks down the field, and no one guards him because he appeared to be an offensive lineman:

4. Vereen, meanwhile, stands around because as an ineligible player, he is not allowed to run downfield:

The Patriots ran the play three times, and they got a first down every time.

It's smart. It probably would not work over an extended time, but when you whip it out in a playoff game in which the defense has no idea what's going on, it is lethal.

The Ravens were angry because they thought the referees didn't give them enough time to match up after the Patriots made a substitution. Harbaugh even took a penalty after the third time the Patriots did this to get the referee's attention. He explained:

We wanted an opportunity to be able to ID who the eligible players were. What [the Patriots] were doing was they announce the ineligible player and then Tom [Brady] would take them to the line right away and snap the ball before we had a chance to figure out who was lined up where. That was the deception part of it. It was clearly deception.

So the officials told me after that they would give us the opportunity to do that, which they probably should've done during that series but they didn't really understand what was happening.

Harbaugh isn't wrong. But there's nothing in the rulebook that says the referees have to delay the play until the defense can get perfectly lined up. By rule, the ref must hold up the play after the offensive substitution only until the defense has had a "reasonable time to complete its substitutions."

As Peter King pointed out in his MMQB column, there was a solid seven to 10 seconds between when the referee announced who was ineligible and when Brady snapped the ball. That qualifies as a "reasonable" amount of time.

The Patriots were triumphant after the game. Tom Brady told reporters:

Maybe those guys gotta study the rulebook and figure it out. We obviously knew what we were doing, and we made some pretty important plays. It was a real good weapon for us.

As Grantland's Bill Barnwell notes, don't expect to see this strategy become commonplace. While it's legal right now, the tactic does go against the spirit of the substitution rule, and it wouldn't be a surprise to see the NFL tweak the rules to stop Belichick from exploiting this in the future.