131 Zone Offense
A good 131 Zone defense can be one of the most difficult strategies for coaches to deal with. Having a go-to alignment and clear in-game adjustments are a must to combat this approach.
The 131 Zone Defense can be one of the most difficult defenses to play against. With good length and anticipation, this strategy can break the momentum of an offense and result in valuable deflections and steals. Perhaps its biggest strength is that it is not something you will see more than 1-2 times per season. It now becomes a special scout for your opponent and in most cases only gives them 1-2 days to prepare for defense. Like all defenses, there are clear tradeoffs with the 131, but if your team can make it a primary focus it has the potential to be a difference-maker.
The focus of this post will be on how I typically like to attack the 131 defenses that I see. Like most of the concepts to try to use I want them to be simple and easy for players to flow into. The majority of what we would work on in practice is the gap alignment, ball and player movement, and then a few adjustments we can make in-game. I am going to go over a few set actions that can be used versus the 131, but in reality, they are only going to be used a few times per game. The majority of the time players will have to flow into our spacing from transition and then look to attack the gaps of the defense.
Post Design:
I. Alignment & Gaps
II. Ball & Player Movement
III. Sets & Actions
IV. Adjustments
V. Wrap Up
If you are interested in running this style of defense or are interested in what the 131 is trying to do on the defensive end, check out the 131 Defense post on my site.

Alignment & Gaps -
My general approach to zone offense, regardless of which type of zone is being used, is to get players into the gaps and attempt to create 2/1 scenarios. We are attempting to get perimeter ball movement for open shots or entry passes into our interior players. Now I do think that good 131 defenses present a challenge to ball movement that most other zone defenses do not. So in our preparation, we need to be more vigilant about players readjusting their gap positioning to make sure that there are passing lanes to the interior of the defense.

Gaps Alignment -
Our default gap alignment versus a 131 defense is a two-guard front with the corners filled and a floating middleman.
Because of the disruptive nature of the top player, I generally want our two top players positioned closer to the lane lanes.
The Corners:
When the ball is in the slot we want our two corner players to be behind the three-point line, positioned at about rim depth. As the position plays out though we want to encourage these players to be creative.
Sneak along the baseline
Flash to the block to catch a diagonal
Make a back door cut when the middle touches, etc.
It's important for our corner players to not just sit in those corners for the entire possession.
"Floating" Middle Man:
It is also very important that our middle man be skilled at finding gaps in the middle of the defense. One of the best ways to create open shots against the 131 is to get those middle touches from the 5. We want him strategically finding gaps and do not want him hiding "behind" the X5, or constantly following the flight of the ball.

Great Question about using Gaps -
This was a good point brought up in a recent Twitter discussion on offense vs the 131. Essentially, the question was challenging whether a 212 alignment is feeding into what a 131 wants.
Explanation:
I always find these questions tough to answer on Twitter because there is usually quite a bit of context that goes with them.
I had some thoughts I wanted to add to that conversation here:
Zone Defenses really force teams into gap-style approaches. Which is ok! We just need to teach players how to exploit the weaknesses of those zones.
Adjustments - I do think there are slight adjustments you can make to exploit what 131 defenses are trying to do; tightening up the slot spacing, adjusting the middle man, getting your corner players to move, etc.
Advantages - 2/1 on the ball side gives you 2/1 on the backside. The 131 is always giving you 2 on the ball, so we should be positioning ourselves to maximize our scoring chances on the backside. In my mind gap spacing is the best way to do that, even if it allows your players to be "gapped" on the ball side.

Ball & Player Movement -
The majoirty of scores we are going to get against the 131 Zone are going to come with simple ball and player movement. In this 212 alignment we want players to know how they can adjust their spacing when the ball is passed to the slot, corner, and middle. We want to hunt for the things that the 131 Zone does not want to see happen; quick swings, touches to the middle, and diagonal scoring passes.

Ball/Player Movement -
Regardless of where the ball is we want to provide some basic options with our spacing;
An Outlet
Diagonal Skip Pass
An Inside Touch Player
Ball in Slot:
The ball will spend more time in the slot than anywhere else. When it is in this position;
Other Slot is Outlet
Opposite Corner is Diagonal
Middle Man slips to the opposite elbow for an inside touch
When the ball is passed from one slot to the other we simply rotate our responsibilities. The the passer becomes teh outlet, the middle man slips to the open elbow, and the corner players flip their roles.
Ball in Corner:
Passing the ball to the corner is a risk/reward versus the 131. A slot to corner pass can present good catch and shoot opportunities, but it can also present good trapping opportunities for the defense. In these scenarios we wants;
Ballside Slot is the Outlet
Opposite Slot is the Diagonal
Middle Man slides to the post, and the opposite corner sneaks along the baseline.
Middle Touch:
One of the negative things about a 212 alignment is that you don't have a player initially positioned at the rim in case a middle touch is acheived. Because of this we need to train our corner players to time cuts to the rim when the middle man touches the ball. I am a fan of letting "cutters cut, and shooters shoot". Essentially allowing our good shooters to spot up in the corner, but encouraging poor shooters to make hard cuts to the rim on thes middle touches.

Middle Man Option -
One decision I wanted to comment on is the placement of the middle man in our gap spacing.
You have two choices with the middle man:
Follow the Ball
Go to Opposite Elbow
Ball Side Positioning:
The traditional approach, at least the way I was taught, was to put the middle man directly into the path of the ball.
Over the years I have found two problems with that appraoch; 1) it prevents any dribble drive penetration from the slot by simply being in the way, and 2) it makes the diagonal pass difficult to see with the X5 & middle man in his line of vision. Coaches may disagree with those critiques but they have led me to take a different appraoch with our middle man.
Opposite Elbow Positioning:
My personal preference is to place him on the opposite elbow from the ball. I think this positioning helps with the previously mentioned critques and also gives us some additional scoring options on the backside. This positoning allows for:
Immediate 2/1 on the backside
Ability to set Back Screen on Top Player
Driving Lane on the touch
Good High/Low passing angle to a Cutter

Sets & Actions -
In scenarios where our players are struggling to find open shots I may choose to go to a set action to give the defense something different to deal with. College coaches probably have 3-4 different "zone specific" sets they like to use. As a high school coach I need to have a much simplier approach to this problem. I like to have 1-2 sets that can be effective against both zone and man defense. Both of the actions we will dive into fit into that category.
Set Actions:
21 Series
Pop Action

Pop Action vs 131 -
One of my favorite zone actions is called Pop Action. I believe it can create advantages against any defemse, but it is especially usefull against odd fronted zones that are weaker in the corners.
I'm also a fan of this action because of how easy it fits with the 212 alignment.