The Defenders Board refers to set ups and covering actions.  Usually we don't say blocks but deflections and coverages.  The purpose of any coverage is to lead to a counter as soon as possible.  So rarely do we use a Defender to try to break someone's arm but usually we are moving away from force and not confronting power.  We use categories on the defenders as well.  Those that move toward the opponent, those that move backward, those that move side ward, those that use two arms and cover a lot of space, and finally knee protection.  Again, while these are not the only Defenders they are certainly vital ones.