According to authorities, Justin Deieso, 35, was off-duty when he got into an argument with Devin Deegan, 55, behind the Terrace Inn Bar & Grill in Whitestone.
Deieso allegedly punched Deegan, causing Deegan to fall and hit his head on the sidewalk.
Deegan was pronounced dead at a hospital later. Deieso was arrested at the scene and is facing assault charges.
Officials are still waiting on results from the medical examiner to determine the exact cause of death.
Get breaking news alerts in the FOX 5 NY News app. Download for FREE!