For many young people sport is a popular part of school life and being in one of the school teams and playing in matches are very important. If someone is in a team, it means that he/she has a lot of extra practice and often spends a Saturday or Sunday away from home as many matches take place then.
When a school team wins a match, it is the whole school which feels proud and happy, not only the players. It can also mean that a school is famous for being good at certain sports and players from that school may later play in professional teams when they grow up.