75-year-old Martin Gugino slammed his head into the ground when he was shoved during a protest in June.
Gugino spent about a month in the hospital with a fractured skull and brain injury.
ALSO READ | Charges dropped for officers seen shoving 75-year-old Buffalo protester
The suit accuses the city of violating Gugino's constitutional rights by enforcing a week- long curfew and using unlawful and unnecessary force.
A grand jury dismissed the felony assault charges filed against Buffalo Officers Robert McCabe and Aaron Torgalski earlier this month.
The city and police department have not commented on the new lawsuit.
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