The subject, best, is best known for basketball.
The article mentions that the school is best known for basketball, indicating that basketball is the sport that the school is most recognized for. This is further emphasized by the fact that the article is discussing a football milestone at the school, implying that football is not as prominent as basketball.
The school’s reputation for basketball is not explicitly stated in terms of its level of success or achievements, but it is clear that basketball is the sport that the school is most associated with.
The article does not provide information on why the school is best known for basketball or how long this reputation has been in place.