This is the 3769th most frequent German word.
rostocker
A "Rostocker" is a person or thing from the city of Rostock in Germany.
In this sentence, 'Rostocker' is used as a noun referring to the people from Rostock, identifying the inhabitants of the city.
Die Rostocker lieben ihre schöne Altstadt.
The people from Rostock love their beautiful old town.
Here, 'Rostocker' functions as an adjective describing the team, indicating that the team comes from Rostock.
Die Mannschaft der Rostocker hat das Spiel gewonnen.
The team from Rostock won the game.
In this context, 'Rostocker' is used as an attributive adjective to describe the beer, signifying its origin from Rostock.