The decision whether or not to restrain a potentially violent person must be carefully and quickly thought out. When involved in a posible restraint situation there are several steps to be considered. The safety of the "target" person, others in the area as well as the the respondent must be considered. In my experience, several steps allowed the process to be effective.
The first step I took was supportive. In other words, try to verbally de escalate the crisis. As long as the "target" person is responding, that effort must continue. However, the supportive time frame might be very short as violence may increase. When this happens step #2 will be implemented. That is when I would take charge of the situation and call for assistance. Anything to avoid handling the situation alone is good. First you have an additional set of eyes, and the second responder can step in to mediate if necessary. If a conflict occurred between me and the "target", I would steps back and my partner would take over. Often this will deescalate the situation. If not, there is more than one person to become forceful.