In a 2-2-1 half court zone, just like in the full court press version, 2 players start high above the three point line just on their own half. The 2 forwards make a box playing on the wings slightly below the 2 guards and the center stays very close to underneath the basket directly. This alignment can seem like a 2-3 zone in the half court however the rotations are different than those of a basic 2-3.
The two high guards at the top of the zone are given the task of forcing ball handlers to the sidelines and forcing traps near the three point line all the way down to the corner. The two wing players below the top guys are tasked with clogging interior passing lanes and being there to create trapping opportunities as often as possible. The center in the middle and under the rim is there solely to protect the rim at all costs and rebound missed shots. All of these pieces fit into a solid defensive line.
The 2-2-1 is a great defense to stop easy penetration and touches in the paint for the offense. It allows for a center to have easy rebounding opportunities and with good wing players above him, transition offense opportunities will come easily as the defense puts the offense into good positions. Mostly, this defense clogs passing lanes and with quick, aggressive players forces lots of turnovers.
The main disadvantage of the 2-2-1 half court press/zone is without a great rebounder down low the defense is prone to giving up easy second chance opportunities. The secondary downfall is a good shooting team can get good shots from the corners and top of the key with good ball movement that leaves the defense vulnerable. However, with a good aggressive team with some athleticism they can create more turnovers than open looks making this defense a good fit for some teams across multiple levels of the game.