Jiu Jitsu is a grappling art. The first thing to learn about grappling is position. Being in a better position means it's easier for you to control your opponent, and harder for them to control you.
There are three components that make good position:
#1 Weapons Facing Your Opponent
Your "weapons" in Jiu Jitsu are any part of your body that can be used to grab, push, or pull your opponent. This means your arms, legs, head, shoulders, etc. If your opponent is behind you, you have extremely limited use of your weapons.
#2 Opponent is "cut in half"
Cutting your opponent in half means to use part of your body to block your opponents mid-section, which limits their ability to use all of their weapons together. Typically, if YOU are cut in half (which means you're in a weak position), you won't be able to touch your elbow to your knee, because your opponents body is in the way
#3 Be on Top
The least important factor of the three, but it makes a difference. Being on top means gravity helps you pin the other guy
This chart demonstrates the basic positions, from best to worst. Keep in mind there are many variants of each position.
A student of Jiu Jitsu must become familiar with the terms for basic positions:
Back control
Mount
Side Control
Guard (and half guard)
The best way to learn position is by practicing Basic Escapes with a partner
Other positions you'll sometimes use:
Butterfly guard
K Guard
Leg Entanglements
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