Any time a hold restricts breathing or restricts circulation it is illegal. However, it it not called illegal in many situations but is either called potentially dangerous (match stops) or just allowed to continue. Many coaches get upset when you let a kid off his back because of a choke hold.
When a wrestler has met near fall criteria a choke or strangulation hold should only be stopped after you have pinned the defensive wrestler. A good official will get this done before the defensive wrestler loses consciousness.
