The 43 Under Defense Part 2: The Leo Defense

 
NOSE GUARD
  The Leo variant of the 43 Under is much more like a traditional 34 Nose Guard than the Tampa 2 Nose. Typically the Leo Nose will line up over the Offensive Center and plays both A Gaps as a traditional Nose Guard would. While the "Tilted" Nose of the Tampa 2 is a quicker, penetrating Tackle, the traditional Nose Guard is usually a huge space eater with wild man strength and lateral agility. His job is to hold down both Gaps and close down on the Running Back if he goes through either of them. The Nose will also eat up a double team to keep the Offensive Line from getting to the Linebackers at the second level. It should be noted that the Nose in a Leo defense will also play some 1 Gap and hold, where he is playing 1 Gap like a 2 Gap. Instead of penetrating like normal 1 Gap defense, he is merely positioning himself in the Gap in an attempt to seal up any holes for the Running Back.

3 TECH
 Just like the Tampa 2, the Leo variant has an Under Tackler or 3 Tech playing between the Guard and Tackle. Unlike the Tampa 2 however, the Leo 3 Techs do a lot more 1 Gap and holding than straight penetrating and are usually a little larger than their Tampa 2 brethren. They occasionally will even play 2 Gap like a Nose Guard.

5 TECH
   In the Leo defense the Defensive End will be a much bigger player, more like a typical 34 end. He may line up in the 5 Tech and control that gap, similarly to the Tampa 2. A lot of the time however, this end will play in a 4 Tech and be head to head with the Offensive Tackle. If he lines up in the 4 Tech he will usually play both gaps on either side of Offensive Tackle. Both defenses also have their strong side Outside Linebacker lined up outside of the 5 Tech End. The difference between the two is more emphasis is put on pass coverage by this linebacker in the Tampa 2 and more emphasis is put on run stopping in the Leo.

WEAK END
 On the Weak side both the Tampa 2 and Leo defense have their best outside speed rushing Defensive End lined up outside of the Offensive Tackle. The Leo defense will usually have their weak side end lined up much wider than a normal 43, in almost a Wide 9 alignment. The Wide 9 alignment is essentially the outside shoulder of an (imaginary in this case) Tight End. The Leo is the glamour position and is the one guy who is not primarily focused on suffocating the run, rather the Leo's only focus is on sacking the Quarterback. The Leo is usually a hybrid player, who is smaller than a normal 43 end but lacks the coverage ability to be a 34 Linebacker. They can (and will) line up in a normal 3-point stance, a Linebacker's 2-point stance, or in either of these two stances, but tilted inward for a better launch angle.

LINEBACKERS
  Despite having the same type of players who play Linebacker in the Leo as in Tampa 2 they are much more run focused, usually reading the pass second. While the Leo will occasionally bring in a speed rusher for the Sam Linebacker to go with a pseudo 34 look, they usually have 3 fast linebackers just like the Tampa 2. The Strongside or Sam Linebacker will usually have outside contain with the Mike(Middle) and Will(Weakside) backers having the the two A Gaps. The Strong Safety will often play up like a Linebacker and provide backup to Sam.

COVERAGE/SECONDARY
   When looking at the coverage in the Leo defense, you have to look at Seattle and two they run the scheme. In Seattle, they run a hybrid 3 Deep/Single High coverage. Seattle likes to bring their Strong Safety up into the box to give an almost 44 look. Out of the base Under front they will have their Strong Safety and Will Linebacker cover the short outside of the field while the Sam and Mike backers cover the short inside of the field. If they are playing a true Single High Cover 1 then they will have their two Corners jam the receiver at the line and cover the flats. If they are playing 3 Deep then the Corners will jam the receivers and then run with them to fill in the deep outside of the field while the single high Free Safety will play the deep middle of the field. Both of these coverages put the Linebackers and Strong Safety in position to stop both the short pass and the run, using their speed and vision. It also puts the Corners in position to give support against the run and lets their Free Safety roam the deep field. While they do not always press, and will blitz or play man to man, these are the base coverage shells the Seahawks like to run when playing zone.
CONCLUSION
  These defenses, for all their differences have quite a few things in common. They both work best when they have aggressive and smart Corners who know when to play the pass and when to play the run. They both utilize three deep coverage shells a good deal, and prefer to get after the Quarterback without having to blitz. And they both demand athletic Linebackers who can swarm to the ball quickly in the run game while covering their zones in the pass game. Both also blur the line between Linebacker and Safety. The Tampa 2 does this with a Mike Linebacker who is essentially a third safety, along with two fast and athletic Outside Linebackers. The Leo defense does this by having fast athletic Linebackers and a big Strong Safety who plays in the box almost as often as the Linebackers do. All in all they are both very strong defenses, and I personally would love to see a team that could combine the two, as they have enough in common personnel wise that a combination of these two could work well.