A diamond press could also be known as a 1-2-1-1 press. One player usually guards the ball out of bounce, 2 players are at the next level guarding whichever offensive players are in the backcourt, 1 player stands around the half-court mark looking for steals and traps, and the final player sits deep to defend easy opportunities at the rim. The middle 2 players and the back of the "diamond" are trying to create traps near half court and create turnovers. The man up front on the ball is trying to create traps near the far baseline and disrupt passing lanes of ball reversals.
An offense who is effective in breaking the diamond press can consistently create easy interior looks and outside shots as well if done correctly. Because of the high risk characteristics of the diamond press, an offense who can move the ball quickly in the backcourt can cause the defense to move out of position and create mismatches once the ball crosses half-court. Getting the ball in and then reversed from one side of the court to the other, coupled with quick movement up the court, should break the press consistently.
The press has a main goal of speeding up the tempo while forcing turnovers. To do this, the defense should force the offensive players into traps along the sidelines, which leads to turnovers whether through intercepted passes or steals from the ball handler. A key to a good press is not allowing easy ball movement around the back court which breaks the press down. By forcing players into predictable dribbling, they will be put into spots where turnovers will almost always occur. All in all, the 1-2-1-1 press or diamond, if run well, can create havoc before the ball even crosses the half court line.