Many fans are concerned with the coaching search producing what they perceive as the wrong candidate. They are not only concerned with landing a bad coach. Some worry about a potential switch back to the 4-3 defense. The Jets switched from the 4-3 to the 3-4 three years ago after Eric Mangini became head coach even though the team lacked the personnel to run it effectively. After spending three years acquiring 3-4 players, these fans are leery of another switch. Some have even cited the trades of Jonathan Vilma and Dewayne Robertson, who were at their best in the 4-3 as reasons.
This apprehensive approach is easy to understand. However, it may not be entirely accurate. Back then, the Jets struggled because they did not have the right pieces in place to run a new defense. A switch under these circumstances probably would work out better. This team does not have the linebackers to run say a Tampa 2 system. Under that scheme, linebackers need to be quick, nimble, and athletic as they must both stop the run and drop deep into zone coverage on passing downs on virtually every play. However, the Jets may find more success in a blitzing 4-3 along the lines of what Steve Spagnuolo would bring.
Vilma and Robertson are gone, but those are sunk costs. The Jets cannot dwell on moves made in the past. They are gone regardless of what defense the new coach brings. One of them, Robertson, was lousy in the 4-3 every year in his career except 2004 anyway. All Gang Green can do is build the best defense it can from this point forward.
Ellis has proven to be an adequate end in the 3-4 due to his size and stout play at the point of attack. It is worth remembering, however, that he put up a pair of double digit sack seasons and his only Pro Bowl appearance in the 4-3, where his primary duty was rushing the passer. His performance in 2008 was his best in years, partially due to Kris Jenkins creating more one on one matchups for him. Shaun would probably be more effective in the 4-3, although he could play in either system.
Jenkins has been an All Pro in both systems. He was dominant early in the season on the nose in the 3-4 before getting dinged up. Jenkins could play either on the nose, where his duties would be similar as in the 3-4, or as the penetrating undertackle in the 4-3. The Jets can expect high level play in either setup, but Kris might be best used as a playmaker whose primary duty is to beat his man, rather than just tie up blockers, which makes the 4-3 an intriguing option.
Coleman would have to move inside to tackle in a 4-3 system. He is solid at the point of attack and decent against the run. He does not really have the bulk to play at nose tackle and lacks the penetration skills to excel at the three technique. Coleman has the perfect height and weight to fulfill the requirements of a 3-4 end, which is defintely his best system. He might be a goner with a permanent switch to the 4-3.
CJ Mosley/Mike Devito
These two are essentially the same player. They are high motor guys who are at their best in one on one matchups. Both played solidly coming in on passing downs but got consistently sealed playing two gaps against the run as backup 3-4 ends. They are built to play the undertackle in the 4-3. It is definitely the best system for both. The question is whether either has the ability to play full time. A rotation of Mosley and Devito at the three with Jenkins on the nose might be the best internal option, but it would be safer to look outside the organization for another tackle.
After coming on strong at the end of 2007 playing the nose, Pouha did not have a good 2008. The run defense stunk when Jenkins exited and Sione entered. He did not do a good job drawing double teams or holding the point of attack. The Jets could look to stuff the run going with a double nose tackle look in the 4-3 of Jenkins and Pouha. Jenkins would presumably draw a lot of double teams, which would make matchups easier for Pouha. His primary duties would be to beat one man and play the run. He could play on first and second down and give way to Mosley or Devito on third and long.
Gholston did not pick up on his new position of 3-4 outside linebacker at all. It seemed like his head was spinning trying to process all of his responsibilities against the run, dropping into pass coverage, and rushing the quarterback while standing up. A switch to the 4-3 may benefit him. He could return to his familiar role of sticking his hand in the dirt and going upfield to hit the quarterback. If the Jets had a big front comprising Ellis, Jenkins, and Pouha, they would not have to be terribly concerned with Gholston's lack of size being a liability against the run. He could just head upfield on every down like Dwight Freeney.
Thomas is not terribly useful in either scheme. Aside from his breakout 2006 season and the first month of 2008, he was a total nonfactor. He might not return regardless of system. In the 4-3, he would return to his original position of defensive end, the first spot in which he busted. He is solid at the point of attack and in stopping the run so he might see some action if the roster remained unchanged and Gholston struggled.
Typically 3-4 outside linebackers convert to end in the 4-3. However, Pace was labeled a bust at 4-3 end early in his career. He only came into his own after moving to linebacker. He did draw praise for his work as an outside linebacker in Arizona when the Cardinals' hyrbrid defense showed a 4-3 front. There is question as to whether he has the speed to handle the position full time. Pace probably would line up as the strongside outside linebacker. He cannot cover tight ends one on one. That would be true in the 4-3, but that would not be much different from where he struggled in the 3-4. He has the strength to redirect tight ends at the line, which would help whoever picks them up. He is also athletic enough to force speedy backs to bounce outside if not track them down, which would make them the responsibility of the corners. He would be lethal as a blitzer. Calvin is very successful coming of the edge, and he would be even tougher as the fifth rusher. He probably could only play outside linebacker in a scheme like Spagnuolo's where he would blitz a lot because that would be the only area his play would be above adequate. He could play the role Spagnuolo envisioned for Matthias Kiwanuka, however. His 2008 success indicates 3-4 linebacker is the best spot for him.
Harris is one of the players most cited in concerns over a shift to the 4-3. This is probably because he has excelled in the same position as Jonathan Vilma. Vilma was great his first two season in the 4-3 and struggled after Eric Mangini's switch to the 3-4. Many are worried the same fate may fall to Harris.He is not a great blitzer, which could be an issue under Spagnuolo. However, there is evidence to suggest he could play the 4-3 well. The biggest issue many cite is his speed. An inside linbacker in the 3-4 needs to shed blocks and stop the run. The 4-3 middle backer has to be more athletic and go sideline to sideline to stop the run. Harris' Draft stock jumped after he ran a 4.5 40 yard dash. While he does not seem to play this fast, it showed he is not a lumbering linebacker. David is weak in coverage, but that would be true in the 3-4 as well. He played the 4-3 successfully while at Michigan Harris is definitely a better fit for the 3-4, but he should be an adequate run stopper in the 4-3.
Barton is a lot like Ellis. He has done an adequate job in both schemes, but his best seasons have come in the 4-3. Regardless of numbers, his best season as a Jet was in 2004 in the 4-3. Either way, the unrestricted free agent probably will not be returning. It does not matter which scheme the Jets use as a base defense. They need to find a linebacker great in pass coverage.
In the end, the Jets will have holes with either front. They will need to get a new linebacker in any situation (inside for 3-4, outside for 4-3). A switch to the 4-3 will likely require obtaining another tackle. Staying the the 3-4 will leave the club with a hole at one of the rushing linebacker positions. Some players profile better to the 4-3, while others are better at the 3-4.
At the very least, a pass rush dependent on Ellis, Gholston, Jenkins, and Pace all facing one on one matchups would probably get more heat to opposing quarterbacks and improve the pass defense in the process. However, the linebackers would not be as effective, even if they were not liabilities
Most defenders will probably give at least decent production in either system. The best fit is probably a hybrid that shows a number of different looks and best utilizes the versatility of its players. The personnel is not in place to have an elite defense with either as a base. Lining everybody up in different spots can help mask the talent deficit to a degree by confusing blocking schemes.