Those responsible include residents, visiting workers, Atlantic Yards site overseers, and city agencies.
I reproduce the first few below, but let me add a conclusion: if construction workers and police officers park illegally, thus contributing to the problem, and if the police won't enforce those rules, someone needs to knock heads.
That someone would seem to be the Empire State Development Corporation, which has overall responsibility for the project.
The 6th Avenue entrance to the arena block construction site at Pacific Street, Sunday June 19th
Pile of garbage under the 6th Avenue Bridge inside the Atlantic Yards Project footprint, Sunday June 19th
Debris under a parked car on Dean Street between Flatbush and 6th Avenues Sunday June 19th. Street cleaning is impossible in this area because Barclays Center construction workers park illegally here on weekdays.