​EAST RUTHERFORD, NEW JERSEY – AUGUST 14: Head Coach Aaron Glenn of the New York Jets looks on prior to the game against the Tampa Bay Buccaneers at MetLife Stadium on August 14, 2026 in East Rutherford, New Jersey. (Photo by Evan Bernstein/Getty Images) | Getty Images The Jets’ search for a new defensive coordinator in the early stages of the offseason had plenty of twists and turns. It ended with the team hiring former Miami Dolphins passing game coordinator Brian Duker to replace Steve Wilks. Duker’s resume was a tad light for a coordinator so it surprised few after the hire when head coach Aaron Glenn announced he would take on playcalling duties.At a few points over the course of the offseason Glenn suggested the team is moving to a 3-4 base defense away from the 4-3 base Wilks operated.Aaron Glenn said the Jets will play a 3-4 base defense with No. 2 overall pick David Bailey at outside linebacker.Glenn, however, has also downplayed any switch to a 3-4 defense.“You do hear that a lot, and I will say this, we are, we will be a multiple defense. So there will be elements of 4-3, there will be elements of 3-4… I don’t want to sit here and say exactly who we’re going to be, because we’re going to be a little bit of everything.”What is Glenn talking about? What do we make of this?Let’s talk a bit about the evolution of defensive systems. I’ll put out the disclaimer in advance that this article will contain some massive oversimplifications for the sake of clarity. When you study football history, you’ll find that schematic innovations tend to have a thousand fathers. There normally isn’t a single inventor of a concept. A few coaches stumble upon something new independent of each other. The new concept works well, and everybody else adopts it. Again, I state this just so you understand that I probably will be leaving out key figures involved with the rises of the schemes I’m about to mention for the sake of clarity.Most football historians have settled on crediting Tom Landry as the coach who took the 4-3 defense to the mainstream. The 4-3 contains 4 defensive linemen and 3 linebackers. (As a good rule of thumb, any defense described by a number lists the number of defensive linemen first, linebackers second, and optionally the number of players in the secondary third. One exception is Buddy Ryan’s 46 defense which was named after the jersey number of a key player, number 46 Doug Plank. We won’t discuss the 46 today.)Landry first used the defense in the 1950s as defensive coordinator of the New York Giants. One of the big drivers in this was the increase in the use of the passing game in offenses during this era. It is disputed whether the Giants were playing a 5-2 or a 6-1 prior to Landry implementing the 4-3. In any event, replacing linemen with extra linebackers provided players who were more adept in coverage against passing offenses, which were becoming more sophisticated at the time. (Another common thread th