Is It Mobility or Stability?
If a joint is restricted the same way every time, that's a true mobility issue. The joint, capsule, or surrounding tissue is genuinely out of range and needs actual mobility work: loaded stretching, joint prep, etc.
If that same joint moves fine when you're relaxed, but locks up the second you're under someone's weight, or trying to use speed, that's not a range problem. That’s a ‘your brain doesn't trust you to control that position under load’ problem. That's a stability issue, and means learning to control the range you do have.
This is a big reason people spend years stretching and see no carryover into life. They’re treating an inconsistent restriction like a consistent one.
The Core Connection:
This is also why stability feels different depending on stance; core engagement is directly tied to your base/foot position, because its job is to stabilize the chain between your points of contact with the mat and your opponent.
When one link in that chain has a mobility or stability gap, your core compensates by dialing down, stiffening locally to protect the weak link instead of coordinating the whole chain. That's why you can feel rock-solid in one stance and strangely hollow and unstable in another that should, on paper, be easier.
Before you spend another cycle foam rolling and stretching, run the test:
Isolate the movement pattern without load/speed.
Compare it to how things behave under load/speed.
Same restriction in the pattern both times = it’s a mobility issue.
Restriction only shows up under load or in specific positions = it’s a stability issue.