Essentially, defense is the activity of neutralizing or reversing the effectiveness of a tactic or resource. The various types of defense I can think of are (includes those already listed):
- scoring denial (blocking or de-scoring)
- game piece denial
- goal denial (whether movable goals or blocking)
- area denial (through obstructions or credible threat of some consequence)
- sabotage (damaging/jamming/entangling the robot; FRC traditionally limits this to extensions beyond the frame perimeter)
- counter-defense (defending against the above actions)
Techniques and tactics of defense include (again, includes those already listed):
- robot-to-robot interaction (blocking, striking, pinning, damaging)
- human player actions (litter, human scoring as a threat to deny area)
- use of game pieces and field elements (moving, throwing, dropping, exploiting)
- Avoidance (being more maneuverable/faster/stronger than will allow the other alliance to execute an offensive/defensive action)
- Hoarding (usually not allowed)
- Sensor disruption/jamming (includes blocking driver/human player vision)
- creating situations in which the other alliance is likely to incur a foul penalty.
Exactly which techniques can be applied to which type is highly dependent on the game design. Also, many of the combinations are explicitly denied by rules most years.