Socially, it can cause a rift between the two. Their friends might take sides. If the boy has male friends, they might get angry at the girl and try to retaliate in some way. On the other hand, some girls might support the girl who kicked, believing she was standing up for herself against a bully. But overall, it creates a very tense and uncomfortable situation for everyone involved.
The girl could get into trouble. If it happens in a school or a public place with rules, she might be disciplined. For example, she could get detention or be suspended. Also, it could damage her reputation among her peers as some might see her as too aggressive, even if the boy had provoked her in some way.