In the movie "Dog Day Afternoon" what does the shouted phrase "Attica! Attica!" mean?

Moretti convinces Sonny to step outside the bank to see how aggressive the police forces are. After a moment, Sonny starts his now-famous "ATTICA!" chant, and the civilian crowd starts cheering for Sonny.

The Attica Prison riot occurred at the Attica Correctional Facility in Attica, New York, United States in 1971.

In the 1975 film Dog Day Afternoon, Al Pacino's character, Sonny, who is holding eight bank employees hostage, starts a chant of "Attica! Attica!" at the massed police outside, evoking the excessive police force used in response to the Attica riot. Many more pop culture references stem from this scene than from the riot itself.

https://en.wikipedia.org/wiki/Attica_Prison_riots

https://en.wikipedia.org/wiki/Dog_Day_Afternoon#References_in_popular_culture