This question was closed as a question answerable from a dictionary:
The double entendre on "balls" is doubtless a dictionary question; but I don't think a dictionary is going to explain the cultural context behind the boldfaced utterance, the use of tickets to the Policemen's Ball as a 'coded' reference to bribery and corruption.
I think the question should be reopened.
ADDED: The question has now been reopened.