For a historical overview of the 3-4 scheme, go here: https://en.wikipedia.org/wiki/3%E2%80%934_defense
The 3-4 scheme relies on 3 large DL who could each absorb a double-team, and LBs who can produce pass rush and run stop.
Running against 3-4[]
There are a few concepts that help attack a 3-4.
- Because the 3-4 is a balanced front, you can overload one side of your line with TE, FB or H-back, creating a mismatch
- In a 3-4, your offensive guards are essentially uncovered by a DL. You can use the free guards to double-team the NT *and* strong side DE with either Inside Zone, power, or dive runs.
- Draws (especially with 3/4 WRs) can be effective against 3-4 packages because the linebackers must spread out and focus on pass coverage.
- Two TE sets (12 personnel) tend to be most effective against the 3-4, as they provide the flexibility to align in ways that overload one side or stretch out the OLBs.
Passing against 3-4[]
The enormous options of blitz packages complicate pass coverage against the 3-4. Rollouts in particular can be risky due to OLB blitzing, or at least on contain.
Playaction throws can be successful for the same reason that draws are successful. If you can freeze the LBs with the PA, it can delay them from getting back in coverage.