Core Mechanics

All techniques in Jiu-Jitsu are combinations of frames, levers, wedges, clamps, hooks, and posts.

The bad news? There are potentially infinite techniques in Jiu-Jitsu, each with dozens or hundreds of details. You'll never remember them all. 

Luckily, you don’t have to. All techniques are comprised of a few fundamental mechanisms made naturally by our body: frames, levers, wedges, clamps, hooks, and posts. These are the core mechanics of Brazilian Jiu-Jitsu.

Once you understand the core mechanics, you'll start to see the commonalities behind all techniques. More importantly, you won't need to remember every single step when applying a technique; you just need to remember to apply the core mechanics. This lets you focus less on rote memorization and more on "filling in the gaps" on the fly. It also allows you to be more creative and modify techniques to suit you, or even create your own.

Frames

Frames are perhaps the most important defense concept in Jiu-Jitsu, and are critical to making the space necessary to protect yourself. Framing means creating a shield with the hard and bony parts of your body to prevent your opponent from closing in on you. Frames are predominantly used from the bottom positions.

Good frames don't rely on muscles, but on skeletal alignment. You shouldn't be trying to bench press or force your opponent away from you. Instead, you're using your skeleton to create a bony shield that keeps your opponent at a distance, and moving your body to create space. Good frames are solid, and don't require excessive strength.

It's also preferable to make frames that don't involve joints your opponent can exploit. For example, if you straighten your arm and try to push your opponent away with your hand, it's easy for your opponent to collapse your arm because your wrist and elbow are weaknesses in the structure of the frame. Framing with your hand is inherently more susceptible to collapse and redirection, but allows more dexterity and gripping possibilities. Similarly, when framing with your legs, it’s usually preferable to frame with your knees or shins; they can support more weight due to a greater surface area. Framing with your feet can be useful as they create a longer range frame than knees or shins, but are more susceptible to being accessed as levers by your opponent.

Levers

Levers are force multipliers, and are the most efficient way to create openings and attack your opponent's body. The levers to the body are (from strongest to weakest): your legs, your arms, and your head. This is the Anatomic Hierarchy.

Using the head as a lever primarily attacks the posture of your opponent, while using the arms and legs primarily attacks structure. See the Theory of Alignment for a more detailed explanation of posture and structure.

Both your arms and legs have three primary joints:

• For arms: Shoulder, elbow, wrist.
• For legs: Hip, knee, ankle. 

Generally speaking, to control an arm or a leg effectively you need to have control of at least two of these three joints. You will be able to generate more leverage by accessing the end of the lever. See: 3 Joint Rule.

When you are on the attack: Lever control is what allows you to advance to more dominant positions and ultimately secure a submission. After all, all legitimate submissions are an attack on one or more levers. See: Isolate a Single Target.

When no one has a clear advantage: Lever control is especially important because the first person to secure a dominant lever will usually control the fight. See: Grips Dictate Position.

Wedges

There are two types of wedges:

• A blocking wedge, which immobilizes part of your opponent's body
• A prying wedge, which pries open your opponent's frame.

Placing your hand next to your opponent's hip to prevent them from re-guarding is an example of a blocking wedge.

The knee cut pass, where you drive your knee through your opponent's guard so he cannot utilize his legs, is an example of a prying wedge. 

Wedges and levers often go hand in hand. In order to control a lever more effectively, you usually need to create wedges on opposite sides of the lever to effectively immobilize the lever. This involves using two-on-one (two limbs controlling one lever) or four-on-one (four limbs controlling one lever) control schemes.

Clamps 

Clamps are made when we lock a portion of our opponent's body inside of a closed circuit. This is a strong control made by clasping your legs or arms together, creating a kinetic chain. This control mechanism acts as an anchor slowing down your opponent, and tethers your body to theirs.

Hooks

Hooks are made with the ends of your limbs. Your hands can be used as hooks, but a more common example is the instep of your foot (shoelace area). This is commonly referred to as a butterfly hook. Hooks create dynamic movements and elevation from the bottom position, and require you to dominate the inside channel. They are also weak, in that they do not act as a closed circuit. This means that hooks can be shut down if your opponent pummels or disengages the hook.

Posts

Posts are used to maintain base from the top or bottom position. They allow for mobility and hip movement from the bottom, and preventing sweeps from the top. When using a post from the bottom position, it is crucial that the post matches the angle of the force vector, or the post will not support the weight of your opponent.

Further study 

• Theory of Alignment
• Solid Frames
• Anatomic Hierarchy
• 3 Joint Rule
• Isolate a Single Target
• Grips Dictate Position
• Kinetic Chains
• Inside Channel Control
• Force Vectors
• The BJJ Formula, by Rob Biernacki and Stephan Kesting