Hitting is not a universal sign of autism but people with autism tend to engage in behaviour that can cause harm to themselves or others when they feel frustrated, overwhelmed or unwell. Some of the behaviours that you may see are banging their head on walls or other objects, hitting themselves or others and hitting their head with their hands. Since some of them lack communication and social skills, this seems to be an ‘adaptive’ behaviour that gets them the attention they desperately seek.