My child deliberately crashes hard into things, bites, or pushes

This can be a sign that their body craves strong input (the sensation of being pushed, pulled, or biting)—a proprioceptive need. If you (1) give them something safe to bite (a chewy tube, etc.) and (2) make "power play" a daily routine—push-wrestling, wheelbarrow walking, carrying heavy objects—you can safely satisfy the craving, and the behavior tends to decrease. If it's accompanied by self-injury, see a specialist.