In the sports world, people get a lot of crap for jumping on a bandwagon of a successful team. In many cases, this is eventually justified, but in plenty of others, it is not and quite unfair. There are a number of other more appropriate labels for fans in this circle.
In recent years, pro teams like the Golden State Warriors, New England Patriots, and Pittsburgh Penguins have been incredibly successful, winning multiple championships in their respective leagues. Other teams like the Chicago Cubs, Philadelphia Eagles, and Washington Capitals have ended championship droughts and their fan support has reached a higher level. The NHL expansion Vegas Golden Knights made the 2018 Stanley Cup Final in their first year, creating an incredibly large fanbase. All of these teams' fanbases have been accused of being "bandwagon" after their success, and that is inaccurate.
In the NBA, with it being such an individually driven league, there are many fans who cheer more so for players as opposed to teams. This is also partially due to some not having childhood allegiance to a team. As a result, there are fans of players like the Warriors' Steph Curry and Klay Thompson who get accused of being a bandwagoner. These fans cheer for the Warriors by proxy of liking specific Golden State players but are not new fans of the team. This is the case with a transcendent talent like LeBron, who has millions of fans who have followed him from Cleveland to Miami back to Cleveland and now to the Los Angeles Lakers.
In cases like the Cubs, who have always had great support even in their down seasons, the term "front-runner" is more appropriate for portions of the fanbase. Many of these fans were not following the Cubs very closely in 2012 when they were at the bottom of the league, but once the North Siders became a playoff team again, they started watching more and wearing Cubs gear. Of course, it would be inaccurate to call all of their fans frontrunners, because many have followed the Cubs their entire life including the franchise's worst seasons. This is also the case for Warriors fans.
In addition, older so-called "bandwagons" like the Dallas Cowboys, New York Yankees, San Antonio Spurs, and Detroit Red Wings have fans that hopped on during the team's glory years and have never hopped off. This makes these people loyal fans now, even if they jumped on at an opportune time. Giving non-local fans of these teams crap for being a bandwagoner is annoying, especially if these people are diehards of said team.
In reality, a bandwagon fan is one who becomes a fan of one team at their peak of success, rides the wave and then hops off the wagon when that team declines and then becomes a "fan" of another successful team. Of course, this practice is fairly common but much rarer than the average sports fan would believe.
Becoming a fan of a successful team is nothing to be ashamed of, especially if they made you a bigger fan of that sport and you stick with that said team even after the glory years. You will get labels thrown at you in conversation, but you are not a true bandwagoner until you leave one team and then start cheering for another at an opportune time.