The individual is introduced to their nation's top sport through family, parents, siblings, neighbors and friends. It may be when a parent or sibling watching an event, a young child might walk past and view on tv. The child will react at first independently, shout and laugh, but will choose a team or player to follow.
Many globally have viewed sports first on the television, smartphone, laptop or any device from the home first. Through increased interest, they purchase tickets (for the most value and affordable rate) to watch live in-person. After attending with friends, family, close relations, co-workers, etc. attention to the sport or team will decline. This may be due to adjustment to the yearly cycle of the sport.
For example, a fan for FC Barcelona beginning first at 10 years of age will view 10 years of highlights, games, training, drafts, trades, coaches, players, club presidents, etc. till the age of 20. Also, in the modern digital age, play video games on the various devices. He/she will not only be a soccer or football fan, but a F1, swimming, chess, cricket, tennis, Olympics, skiing and any of the various hundreds games created.
But as the fan understands the seasonal cycle and stories, the fan will lose interest in one or all sports. Scandals, poor playing, cheating, too much losses or wins too have a mental effect for fans. Poorly playing teams and lower tier will have fewer attendance than top tier teams. Fans might choose, during low periods another team or sport to support and view. Life might also occupy the individual with higher responsibilities to education, work, love partner and creating and maintaining the family.
Since the beginning of evolution, creatures have changed their living environment from the oceans, land, air and finally space. Similarly humans change to adjust their zone.