A blog article provides a useful progression to think about defending in volleyball, though there are some fuzzy points in the systems side.

A fellow volleyball coach highlights a weakness of heat mapping to help decide what type of defense you play

At what point does it make sense to dedicate a defender to take tips, and thus forgo defending spiked balls?

Is it best to get great at one defensive system or to develop the ability to play multiple systems? I argue doing the first is…

Making your team strong in defense generally means addressing four primary areas of focus - blocking, system, digging, and mentality

How important is blocking in determining a volleyball team's success? It depends on how you define blocking and the level of play your team is…

The ball-setter-ball-hitter visual cue progression for volleyball blockers allows them to properly position and time their blocks.