Fighting is an extremely social behavior, particularly in the context of adolescent males. It represents a high degree of concern for honor, status, reputation, justice, the in-group, etc - high enough to risk physical harm. Someone (like me) who has never been in a fight is far less social, less engaged, more apathetic about peers and their emotional lives, than someone who will throw down when they feel it’s appropriate. In this case, that lack of concern for social status is positive, but stil.
Fighting is not isolation taken to an extreme, it’s the opposite.
You're taking antisocial as a colloquial term. When discussing antisocial behaviors in terms of psychology, fighting is will almost always be antisocial.
But also probably for pulling fire alarms repeatedly, petty vandalism, cussing people out, etc. Not your actual violence, but still acting contrary to how we expect people to generally act in society. Which is also different from simply not interacting with people very much.