Skyler Cassity, Defensive Coordinator at North Texas, teaches Cover 3 as a complete vision coverage.  They do not look at routes, they read the quarterback's shoulders and eyes and aim to make him throw into tighter windows.

The video below was recorded when Coach Cassity was the DC at Sam Hoston State before he moved to North Texas.  It is a portion of his presentation on Cover 3 Progression for DB's & LB's out of Even & Odd Fronts.

Key Defensive Principles:

• Run Gap Responsibility: Outside of "number two" receiver
• Defender's position determines gap assignment
• Handle different formations, motions, and shifts through consistent rules

Pass Coverage Techniques:

• Initial aiming point: 12 yards, top of numbers
• Primary goal: Eliminate vertical routes
• Use wingspan to reroute receivers
• Reroute anything within defender's wingspan

Coverage Progression:

1. Initial Reroute

• Punch out at exit angle
• Keep vision on quarterback
• Practice from field and boundary perspectives

2. Route Reading

• Don't focus on routes
• Read quarterback's shoulder progression
• Break to flat when quarterback's shoulders cross defender's face

3. Underneath Zone Strategies

• Four underneath defenders work together
• Progress in coordinated movement
• Use "five-yard no-cover zone" to let routes distribute

Key Teaching Points:

• Defenders should get information from quarterback
• Be prepared to drive on checkdown passes
• Create opportunities for turnovers and big hits
• Understand gap responsibilities and leverage

Defensive Goals:

• Keep ball in front
• Limit vertical passing threats
• Maintain coordinated underneath coverage
• Adjust to different offensive formations