I'm not saying that one is better than the other, just that there is an important difference.
What is the difference between the two?
Well, it's in the words. A fan likes something, a supporter actively supports it. A regular fan would not drive 5 hours to support the FC Bayern Amateure in the cold March rain.
What do Supporters do differently?
Passion. Dedication. Loyalty.
Take a club like Bayern Munich for example. We have by far the most fans in Germany, but only a small group of true Supporters. The fans buy lots of merchandise and visit the home matches, and usually refer to the team, not the club. The fan idolizes players, but often knows little about the club's history. When a club does not do well, more and more seats will be empty, where the section of the Supporters is as full as ever.
A Supporter loves the club, not the team and its players. Those are mercenaries who do not identify with the club and will transfer as soon as more money is offered.
To a Supporter, it's all about the club, not the team.
A fan sees this as a hobby or casual entertainment. But Supporters take it seriously. No matter where or when the club plays, or how important the match is, the Supporter is there. A lot of times this means sacrificing other aspects of his life – work, school, family, friends. That's because words like loyalty and honor still have meaning. A Supporter will defend the club's name if necessary, without getting it into trouble.
To the Supporter the club is a lifestyle.
The Supporter supports the team throughout the entire match, regardless of the score or the performance. Because the team needs the support the most when things are not going well. That is not to say that displeasure can not be voiced. But the support of the team always comes first.
Simply singing or shouting is not enough. Every word uttered and every song sung has to be filled with all of the Supporter's energy and passion. Even if the players on the field do not care, it is done for the club's honor and for all of the Supporter's honor.
Sing until your lungs burn and you are ready to puke.
Supporters looks at everything the club does objectively and is not afraid to be critical. It is up them to protect the club's values and integrity and to carry them on with their actions.
Should a decision of the club clashes with the Supporter's believes, but benefits the club in the long run, the Supporter has to put his own interest aside.
Everything the Supporter does has to be in the club's best interest.
All of these routes are vital. I have known people who went to every FC Bayern match, but did not support. There were those who sang passionately, but only cherry-picked a few matches a year. Not to mention the ones that were too drunk to even make it into the stadium, or those who only want to fight.
Unfortunately there seems to be a war going on against the Supporters / Ultras across Germany. The clubs want to replace us with customers who will shell out money without asking questions or criticizing. The clubs' identities are slowly taken away. But this is for another article.