Backhand force, 1 is the rabbit, chasing the disc and always putting on the mark; 2 and 3 are the mid wings, each patrolling one side of the cutting area and taking away any threats; 4 is the deep, responsible for taking away deep threats but can pinch if nobody is deep.
2 and 3 take the biggest threat on each side, ideally putting max pressure on short passes that would gain easy yards. 4 has to mark any deep threat but can pinch to help when appropriate.
If the offense gains yards (e.g., pass to the handler cutting across), the zone resets on the disc. 4 is always ready to cover any deep cuts.
If the offense advances the disc much past half, the deep will call out "melt" or "wall", meaning it's time to collapse into a wall across the endzone.
In the wall, the two wings collapse to defense the endzone with the deep, while the rabbit does the same job as before (it might be easier on the rabbit to force *outside*) from this point on.
It's fine for the offense to complete passes like this -- the goal is to force lots of passes and, eventually, turnovers due to risky, frustrated scoring attempts. It's important that the wall stays put, not being tempted off the line by passes close the endzone (sometimes there are obvious chances at a D here, but mostly the wall should stay put). Note that there's not usually such a deep endzone to worry about in 4v4. Communication among the wall members (and from the sideline) is vital for keeping track of cutters behind.
Here, the handler successfully swings the disc, but nothing changes for the wall -- they must stay aware of players leaving the endzone and moving from one 'zone' (i.e., one of the defenders territory) to another. Mark forces outside again to cut down on running/seal things easier.
One common scoring play is a handler cut upline, receiving a short pass while jumping into the endzone. If the closest wall member sees this coming and challenges it, the others must compensate because the alternate scoring play here is to throw it to a deep cutter who has been left open due to the challenge of the upline cut.