These 2 defensive drills come from Xavier.
You can see their archives at this link.
I hope you are able to modify one of these drills to help your team.
I like the idea of timing the players as they are converting to defense.
4 on 4 Defensive Conversion Drill
1. The drill begins with live four on four action taking place at a basket. On the shot by the offense or the command of “change” by a coach, a conversion takes place. If a shot is taken two forwards or bigs attack the offensive glass while the two guards get back on the shot. A coach is assigned the offensive rebounders and a second coach is assigned the two guards “getting back.”
2. On the conversion, all four defenders must cross the halfcourt line in 2.5 seconds or the drill stops and the four converting defenders will run. Editor’s note from Brian: IMO, this is the most significant takeaway from this post–giving your players a specific standard of what getting back quickly means to you as a coach.
As the drill continues the defense gets set and live four on four action takes place at the other end. Once again, on a shot by the offense or the command of “change” by a coach, a conversion takes place. There is no out of bounds. This action takes place for several minutes. The coaches are paying particular attention to offensive rebounding, getting the guards back on the shot and making sure all four defenders cross half court in 2.5 seconds or less.
3. To ensure more shot attempts the shot clock can be shortened for the offense promoting more rebounding opportunities and more conversions.
4 on 3 Offensive Movement Drill
1. The drill begins with a coach having the ball on the baseline under the basket. Three defensive players are facing the coach. There are four offensive players surrounding the three point line.
2. The coach passes the ball to one of the four offensive players. On the catch by an offensive player the offense can move anywhere in the halfcourt. Each offensive player is allowed two dribbles.
3. The three defenders closeout on each catch by the offense and begin to work together. One of the three defensive players must be guarding the basketball at all times. On a shot by the offense it is a four on three rebounding advantage. The defense must find a way to rebound the ball.