The threshold
Physical intervention is justified when necessary to prevent imminent harm to a person, to prevent a crime, or to remove a trespasser after lawful request to leave has been refused and the situation cannot be resolved otherwise.
Positional asphyxia — the risk nobody trained you enough on
Restraining a person face-down or with pressure on the chest can kill within minutes. Reposition the person on their side (recovery position) at the earliest safe moment.
Post-intervention duty
Medical check offered every time, ambulance called for any head impact or breathing concern, incident report within the hour, witnesses identified, CCTV preserved.