The 2-1-2 half-court zone defense leaves 2 players on top, 1 in the middle, and 2 down low. The top players are usually the guards with the center in the middle and the 2 forwards playing low. This defense at first glance can look similar to a 2-3 zone however the assignments and roles are a little bit different.
The guards on top of the zone have two main roles: take away passing lanes and prevent dribble penetration. They must effectively keep players in front and with few options. The center in the middle must keep players from getting into the post around him and to take away cross-court looks. The forwards play the ball in front of them, defend the corners, as well as preventing the ball from entering the post where they are likely to get easy baskets.
The two major strengths of the 2-1-2 zone are ease of rebounding out of the set and limiting shots from the paint. Because the 2-1-2 is a generally compact zone, it allows for easy rebounding and for paint shots to be much more easily prevented. It also makes slowing the pace of the opposing team's offense down as it prevents the easiest shots from being made a high rate.
The one major weakness of using a 2-1-2 is its relative inability to limit perimeter shots. If a good shooting team starts to make a lot of outside shots the 2-1-2 cannot begin to prevent them without opening up holes on the inside so a switch in defensive strategy may be needed. Overall, the 2-1-2 prevents easy interior shots and allows for easy rebounding opportunities making it a good defense for younger teams to use.