re: What's the difference between a 4-3 and 3-4 defense?

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Here you go. Knock yourself out.

LINK

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Thanks for the link, but it doesn't address my question at all. LSU ran a 3-4 with one OLB consistently playing at the LOS.

Couple things I haven't seen explicitly mentioned in this thread yet:

+ The 3-4 has more speed than the 4-3 owing to the replacement of a lineman with a linebacker. Probably an obvious one, but worth noting, as it's one of the biggest reasons for the increase in the 3-4's popularity in recent years. You put more speed on the field to make your life easier defending the pass. The tradeoff in sizing and added demands on the defensive line in plugging gaps can make the 3-4 worse against the run--certainly it's simpler to plug the same number of gaps with 4 linemen instead of 3--but at a top tier program like LSU, with the ability to find the best athletes and coaches to train them up, this is a more abstract than real tradeoff.

+ Against the pass, the most frequent number of rushers a defense will send is four. In a 4-3, the four rushers will all be the defensive linemen in the vast majority of situations. In a 3-4, they will be all three defensive linemen, plus a linebacker. That flexibility in choosing which linebacker to send makes the basic 3-4 harder to predict.

+ It's also more common for a 3-4 to drop 8 into coverage than a 4-3, so while both formations can do it, the 3-4 is a bit better equipped to leverage that option, again adding to the possibilities. Dropping 8 is pretty uncommon in general so this is a minor point, but highlights the flexibility of the 3-4 compared to the 4-3.

P.S. Sorry about the guys teeing off on an "obvious" question. I've found it surprisingly difficult as someone who didn't play football growing up to find good resources explaining the finer points of football strategy. I think it's pretty clear you know that a 3-4 has 3 linemen and 4 linebackers and a 4-3 has 4 linemen and 3 linebackers and just didn't know what the non-obvious strategic implications of that difference were, and sadly a lot of people would rather pretend you're a dumbass to feel better about themselves than provide that insight.

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Google it yourself and you will find what you're looking for faster than waiting for an answer here.

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Because few, if any, here know, which I find hilarious with all the talk of 3-4 or 4-3 personnel flying around here because of Aranda leaving.

Everything as far as in the box goes. There's no difference in coverage or as far as the dbs are concerned. You are asking your front 7 to do different things and have different roles in the two philosophys. The main thing is that you have no noseguard in the 4-3 like you do in the 3-4...which is why I prefer the 3-4. We are suited to run the 3-4 right now and I expect pelini to run that until we get the personnel he needs for the 4-3. Basically there's a difference in defensive alignment and what you are asked it your defensive ends or olbs to do. A 3/4 defensive end/olb has to be able to drop back in coverage and cover passes in the flats slot of times. It's a completely different philosophy and is more complicated than just having an extra lb on the field and one less defensive linemen. The 4-3 means you have two defensive tackles, two defensive ends, 2 olbs and 1 mlb. The 3-4 means you have a noseguard, two defensive tackles, 2 olbs and 2 ilbs. The 3-4 is more versatile then the 4-3 though and allows you to use your players athleticism more, especially when you have the type of athletes at the olb/defensive end spot that LSU always has. Totally different schemes in the front 7 and you have to recruit completely different for the 2 schemes.

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+ The 3-4 has more speed than the 4-3 owing to the replacement of a lineman with a linebacker. Probably an obvious one, but worth noting, as it's one of the biggest reasons for the increase in the 3-4's popularity in recent years. You put more speed on the field to make your life easier defending the pass. The tradeoff in sizing and added demands on the defensive line in plugging gaps can make the 3-4 worse against the run--certainly it's simpler to plug the same number of gaps with 4 linemen instead of 3--but at a top tier program like LSU, with the ability to find the best athletes and coaches to train them up, this is a more abstract than real tradeoff.

+ Against the pass, the most frequent number of rushers a defense will send is four. In a 4-3, the four rushers will all be the defensive linemen in the vast majority of situations. In a 3-4, they will be all three defensive linemen, plus a linebacker. That flexibility in choosing which linebacker to send makes the basic 3-4 harder to predict.

+ It's also more common for a 3-4 to drop 8 into coverage than a 4-3, so while both formations can do it, the 3-4 is a bit better equipped to leverage that option, again adding to the possibilities. Dropping 8 is pretty uncommon in general so this is a minor point, but highlights the flexibility of the 3-4 compared to the 4-3.

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Thanks for the serious answer. It seems 15+ years ago 4-3 defenses had 300-320# DTs and 280-300# ends but in the early 2010s I noticed LSU move to smaller WDEs going as small as 240#. Now in a 3-4 we're using a 250-260# "OLB" to do the same thing the WDE was doing, from the same spot on the field.

With the proliferation of spread/RPO offenses and the lack of a fullback in modern CFB, I am having a hard time differentiating between the 4-3 WDE and the 3-4 rush LB.

A down lineman and a linebacker

Lol, it's alot more complicated than that...though your answer is correct when simply talking from a personnel standpoint.

You have to consider how each alignment/personnel package is going to account for all areas of the field and what the offense will run. Therefore, you ask different assignments out of the olbs and defensive ends in both schemes. The 3-4 allows you to be more aggressive in my opinion and is more versatile, especially when we get the type of freak athletes that LSU does.

Exactly right. Defensive ends nowadays aren't going to be the Tyson jackson type bc you have to have a barkevious Mingo or chaisson in that position.

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olgoi khorkhoi

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What's the difference between a 4-3 and 3-4 defense?

3-4 defense has more flexible options allowing more athletic players playing linebacker and outside rushing options confusing the QB's and most likely the better defense against the RPO offenses of the modern football offense.

Basically you have a nose tackle with two interior linemen or DE's and two middle linebackers and two outside linebackers.

The 4-3 defense will clog up the middle and most likely better against a power rushing offense.

Like everyone is saying research a little and determine the defense you would employ against the modern offenses of today.

Depending on personal chose your defense but most teams in the NFL and great college defenses today are playing a 3-4