Grand Theft Auto: San Andreas/Beat Down on B Dup

For this, go with Sweet to B-Dup's apartment, and then to Glen Park. Provoke a gang war, win, and kill the Ballas around B-Dup's house. Watch the cut-scene, and Mission Complete.

Tips
I recommend starting the gang war from the tunnel walkway in the northern middle of the park where the police badge is. By using the sniper rifle you can kill the gang when they are far away, and the police won't notice you and cause trouble.