I am significantly less worried about him putting himself in danger of a further attack than I am worried about him becoming too aggresive. the line is very fine.
Fists forward... Agressivity in children is natural, and even needs to be expressed. Pushing, pinching arms, cheeks, kicking, pulling hair are common to all children. However, they don't come out of nowhere. In most cases, conflicts are about possessing an object, a toy, about going down the slide first. Agressivity can also manifest itself when a child was denied something, did not get an answer upon a question, or when he/she is bothered during voluntary or forced isolation. Opposition to what is forbidden, inability to deal with frustration. I suppose a stressful family situation or a lack of affection might make those manifestations more frequent. All children fight, but some make it their preferred means of expression. And that behavior leads them to be excluded. Isolation is unbearable to them, which in turn leads them to be even more aggressive. Pretending indifference is the worst of solutions, as children need to be listened to, recognized. A child needs to be protected from his/her own violence, and it is up to the adults to set the limits so that they can better adapt to the real world. Language acquisition helps. But aggressivity must always be expressed, as damage from repressed feelings can cause deeper suffering.