Title's pretty self explanatory. There can be an influx of them during the post season, regular season or the finals regardless of what sport the team belongs in.
For me, The Houston Rockets. I HATE their fans. Seriously, after watching Game seven of the NBA semi-finals I'm fully convinced I've seen more bandwagon fans than Clippers and Lakers fans. They're a good team I'll give them that as a Loyal San Antonio Spurs fan but I hate their supporters.