Question, can we restrain somebody who's in immediate danger?
Answer, we can use force for a number of reasons, to prevent harm to ourselves, to prevent harm to others, to prevent damage to property, and to prevent a crime. So for example, if somebody's in imminent danger, let's say, of self-harm and we feel we haven't got time to try and talk them out of it, then it may necessitate the fact that we have to go in and physically intervene, restrain the person. So we think about preclusion. If we don't act immediately, then that harm may be realised and the person suffers injury.
What covers this? Well, common law, because we think about it, what we're doing is in the person's best interest. So yes, we can use force to restrain somebody if they're in immediate danger.