These two defenses are used for one of two reasons; either your opponent has a prolific scorer you want to slow down or your opponent is much more talented than you.
They are commonly called “junk defenses” since at times they give less talented opponents a “fighting chance” since most teams do not practice against these types of defenses.
Box and 1
The box and one is used most often to shut down a scorer or take a team out of rhythm. Four of the five defensive players play zone defense. They cover the four corners of the lane; two at the high post and two at the low post, hence the name box.
The fifth player plays man-to-man and usually covers the best scorer or best overall player on the opposing team. The rotation of the box is quite easy. If the ball is passed into the corner the low post defender covers the corner and the opposite low post defender comes across to cover the low post on the ball side. The two defenders on the corners of the foul line do the following; on the ball side that defender slides down the lane a bit, but not far and watches for cutters through the upper part of the lane, while the defender on the opposite side moves down into the lane and covers the middle of the lane as if it were a 2-1-2 defense. Of course, through all this the one player playing man defense stays “glued” to his man.
Diamond and 1
The diamond and 1 is just a hybrid of the box and one. The four that play zone are lined up as follows; one at the top of the key, one on each of the corners of the free throw line or just below it and one in the center of the lane just above the basket.
The rotation for this is similar to the box and one and depends on the coach, but if the ball goes into the corner the wing on the foul drops to the low post, the opposite wing drops into the low post, the player underneath the basket goes to the corner to cover the man with the ball and the player at the top of the key drops to the corner of the foul line.
All the while the fifth defender is covering the scoring threat like a glove.
The coach needs to know when to use these “junk” defenses. The box in one for example is not good against a team with a very good low post player.
That player will be guarded man to man and you will have another player that is one the post and it will create an unbalanced defense.
So the best time to use the box and one is to stop a shooter. With the shooter playing the perimeter the box can effectively keep the post and lane covered and the one person playing man can dedicate themselves to sticking with the shooter. If these defenses are executed well and used at the right times, then they can cause enough distraction and problems to take an effective offense out of their rhythm.