Mailbag question regarding the difference between 3-3 defense and 5-3 / 4-3?

Got an e-mail from Grant:

Hey Coach how does the 3-3 differ with the 5-3 / 4-3 in basic alignment?

CoachBt: 3-3 can be made to look like 5-3 by simply moving SS's up to line of scrimmage. Big difference is in 5-3 you use different type of personnel. You use a bigger stronger, personnel in 5-3.

3-3 is a hybrid 5-3 using extra DB's to give defense more flexibility. As for alignment, in 5-3 and 3-3 you generally have a NT cover the center, and two DT's who either play in four or five techniques. four tech means DT's are in B gap or between OT's and OG. In five technique DT's line up head to outside shade on OT.

Both defenses also have a MLB who stacks behind the NT. Both also have two OLB's who can stack behind the DT's in 3-3 but can be either stacked behind DE's or line up in an inside or outside shade on DE's in the 5-3.

In 3-3 instead of DE's you generally have the two safeties in place of DE's. These DB's/safeties give 3-3 more flexibility in alignment than in 5-3 and usually adapt depending on offenses formation. The back 3, 2CB's and FS generally will play three deep in base for both defenses, but depending on blitz package you can man up.

One big advantage to 3-3 is ability to play some sort of two deep coverage with either man under or five under similar to Tampa 2. This is very difficult to do in 5-3. Your OLB's will generally be no match for either slot or athletic TE's in coverage.

4-3 is completely different front and scheme. In base 4-3 you line up with DT's covering OG's and DE's covering or outside shade on OT's. They still use MLB covering center and have OLB's to cover TE's or stacked to outside shade on DE's. However in 4-3 your MLB is generally not stacked behind a D-Linemen. Secondary is completely different in 4-3, because you have only four DB's. You do not have the flexibility a 3-3 has and having SS allows you roll the secondary either to the strength of the formation or to the wide side of the field.

Thanks for writing in and hope you understand the basics of these defenses and formations better.