Prosecutors asked a judge to drop the charges after concluding they could not disprove beyond a reasonable doubt that Tate's actions were justified.
They said surveillance video supports Tate's story that he bumped into 55-year-old Eweka Johnson as they walked past eachother on the subway platform.
They said Johnson pushed Tate, would not back down, and an argument ensued.
Tate threw one punch and walked away.
Johnson remained upright but about two minutes later, he fell to the platform and was pronounced dead later that night.
An autopsy revealed the cause of death was a ruptured cerebral artery aneurysm.
Prosecutors said Tate likely could have established his actions were justified at trial, and video surveillance largely corroborates his account.