Officers were called to Maryhaven Center of Hope, located at 222 Currans Road in Middle Island, around 9 p.m. after a resident became uncontrollable and violent.
Maryhaven employees requested the resident, 29-year-old Dainell Simmons, be transported to Stony Brook University Hospital for a psychiatric emergency.
Simmons reportedly fought with the officers, who made the decision to use the taser and pepper spray on him.
During the struggle, Simmons became unresponsive. He was transported to John T. Mather Memorial Hospital in Port Jefferson, where he died.
Lieutenant Jack Fitzpatrick told reporters Thursday that Simmons was acting "violent and uncontrollably" and that the decision to use a Taser appeared appropriate under the circumstances.
Multiple police officers were treated and released from various hospitals for injuries sustained during the struggle.
Simmons, who was 5'10" and 240 pounds, was taken to the Suffolk County Medical Examiner's office, where an autopsy will be performed.
Homicide investigators were at the scene for more than six hours trying to get information on what happened, and nearby streets were closed off during the investigation.
This is the first incident reported at the group home, and neighbors say they've never seen police called there before.