This is a 3-3-1 defense, but NOT a cup. It
seeks to clog the middle of the field by having one mark on each
handler, forcing middle. The middle handler mark ("Clamidia")
always seeks to prevent continuation in the same direction that the
disc was swung. All handler marks Poach out into the forced lane when their
charge does not have the disc, but must still be able to recover and
do their primary job when the disc is swung.
The second three are always forcing a cutter Out, essentially
playing Person defense unless called off by the deep, or unless the
cutter becomes a handler. Note that they may need to switch
the side they are marking if a handler mark is broken.
Finally, recognize that this works even better when the offense
starts in Vertical stack instead of Horizontal. Everyone's job
is still the same, but Clamidia's job is much easier as there is no
need to recover without a middle handler: