This depends on the clients age and ability. Before the challenging behavior there is a trigger, or antecedent. ASD students have problems with anxiety which can trigger aggression, so planning slow transitions is important. Also making sure there is a schedule in place, they are earning rewards for appropriate behavior and have plenty to keep them busy doing what they enjoy. I'd say too, there should be meals and snacks at regular times so the client isn't uncomfortable because they are hungry and thirsty. If the client still becomes aggressive this isn't a teaching moment. Say as few words as possible while giving directives such as "stop", and "Go to your safe place."in an authoritative voice and be sure the directive is given and has been taught "Hands to self," Hitting, biting or kicking are not okay". One of my students I needed to hold and speak calmly, "Your okay. Deeper breaths". Otherwise, he would harm others. Especially those smaller than him. Then I would get him to come with me to a different space until he was regulated. Another student needs lights out and complete quiet for about ten to 20 minutes. Ultimately a relationship needs to be in place first so a client trusts me and so will take direction knowing it is the right thing to do to be safe and show care for themselves and others. They feel bad when they are angry, but they don't have to feel bad about what happened during or after if they handled it properly. Offering lots of praise after the fact for handling hard feelings without harming themselves or others is important. It's hard and it's a big deal and I say so.