HSV (pronounced Haa Ess Fow) is Hamburger Sport-Verein. It was formed by amalgamating 3 clubs in 1919, although you will often see the year 1887 quoted. This is because one of the clubs, Sport Club Germania had been founded in 1887. It seems these things are important to Germans!
Although HSV is most famous as a football club, as the name suggests they are also involved in many other sports. They have Athletics, Ice Hockey, Handball, Tennis sections. They even have a cricket section!
Their logo is instantly recognised throughout Germany and amongst football cognoscenti throughout the world, and is known simply as Die Raute (the diamond). Wherever you go in Germany, people will recognise Die Raute and greet you, sometimes even in a friendly manner!
Their homepage contains an informative English language section www.hsv.de