Early in my career a coaching friend of mine told me that the head coach he worked for did nothing but scrimmage the entire practice.
I remarked to my friend that this seemed like a poor way to teach the game, an inefficient way to master an offensive or defensive system. To my surprise, he told me his boss was one of the most successful coaches in Illinois basketball history. Yet I still believe this coach's success was in spite of his scrimmage based practices, because pure scrimmaging allows relatively little opportunity for giving feedback. His teams eventually learned what to do (after all, if you scrimmage for 2 1/2 hours every day, you'll eventually figure it out!) But this haphazard, unfocused, inefficient, approach meant that practices ended up being far longer than they needed to be!
On the other hand, we've all known coaches who are "Drillmasters." They disdain scrimmaging, and break the game down into the smallest detail, and yet the teams they coach somehow never seem to reach their full potential. Tell them their team has a problem attacking the press, and rather than working against the press, they create a press-attack breakdown drill. They are so focused on teaching the fine points of the game that their team never learns to play the game! I knew one such coach whose players were the most fundamentally sound of any team in our league, yet they routinely finished near the bottom of the conference standings, because their mastery of individual fundamentals never seemed to translate into solid team play.
Could it be that the correct approach is somewhere in between these two extremes?
For example, yesterday I mentioned that we'd simplified our practice plan in order to address the problems we were having with running the floor, and with trapping on a missed shot. We decided to spend 30 minutes on one drill that addressed the two major problems we'd been having. We call this drill "5/5 Blockout," but a more accurate name might be "5/5 Blockout, Break, and Press."
We start by having a coach shoot, while Team A blocks out Team B. Team A rebounds the miss (or inbounds the made shot), and breaks to the other end as Team B falls back into a half-court man or zone defense. If Team A scores, they will immediately move into their full-court press against Team B. If Team A does not score, they run our Missed Shot Press. Team B attacks the press, and play continues until Team A again gains possession following a rebound or score. We then substitute and reset the drill, using the interval to discuss any corrections that need to be made. Eventually, after we've learned the drill, we will begin keeping score using the game clock, awarding 2 points for a trey, 1 point for a basket inside the arc, and playing to 5 or 7 points. Alternately, we might just see who is ahead after playing for 10 minutes.
The reason I'm going into such detail here is that I think this sort of situational scrimmage drill work is exactly what a team needs to master System basketball. By never going more than 1-2 cycles, we reap the advantages of using a live, realistic scrimmage format, while still allowing the coach to give continual feedback to players after each "bout."
Yes, players can improve by simply scrimmaging for the entire practice, and they can improve via breakdown drills. But when players are learning a new system, I have come to believe that the most productive way to practice is the "whole method" controlled scrimmage. They need to see the big picture, and you need to correct them as they execute realistic game situations.
Sure, you do need to occasionally break down your offense/defense into its parts, and drill those parts! But you also need to break the complete game down into its situational parts, and drill those 5/5 situations using 1-2 cycle controlled scrimmages until players have mastered them.
Fast break after a score... press after a missed shot... offensive attack following a dead ball... defending an opponent who is trying to hold the ball on you. Create 5/5/ drills to work on these situations, while making sure your team is also leaning to convert defense-to-offense and offense-to-defense.
Master the situations, and you'll master the System.