Police in the town of Starnberg said Friday that the 15-year-old teenager was detained after a security guard at Thursday night's party called authorities when the boy asked for drugs and turned aggressive.
Some 100 teenagers then went to the precinct and broke a window. Around 50 of them tried to free the boy, whose name was withheld in line with German privacy rules. German news agency dpa says police from nearby stations were called in to calm the youths, two of whom were temporarily detained.
The boy then complained about headaches and was taken to hospital.