It happened around 2 p.m. near his residence on East 10th Street in Manhattan.
Police say the actor punched someone who took a parking space he was attempting to hold for himself.
The space is right outside his building on East 10th Street.
Baldwin was placed under arrest and is now at the NYPD's 6th Precinct.
He is expected to be charged with third-degree assault.
More information will be posted as it becomes available.