The offense has the disc near our end zone, the deep has already called melt and everyone has found a player to defend. The mark or in this case "1", sets the force (in this case flick) and all the downfield defenders line up on the open side of the player they are guarding, taking away the under, while the other handler defender takes away the deep
One of the players on offense cuts, the player guarding them stays on the open side and forces them to go to the break side.
The cutter returns to the stack or goes to the break side and the field is essentially reset.
If the reset handler is activated (later in the stall count) and attempts to run upline, the defender holds their ground and stays on the open side.
If the handler then attempts to receive a reset, their defender (in this case 2 follows them close enough to get a d if it is thrown but not too tight as to give up the upline.
At this point, the stall count is probably high and the thrower is most likely no longer looking up field- this is when the mark should mark HARD NO BREAK/AROUND/RESET and stop that reset from being thrown