John Saunders' Wife Called 911 After Founding Him Unresponsive

John Saunders' wife found the ESPN legend unresponsive and not breathing early Wednesday morning and called 911 ... law enforcement tells TMZ Sports.

Hastings-on-Hudson Police Chief Anthony Visalli tells TMZ Sports ... emergency responders raced to Saunders' New York home around 4 AM -- but were unable to resuscitate him. He was pronounced dead at the home.

We're told a detective was sent to the home -- but found nothing suspicious. Since there were no signs of foul play, the medical examiner rejected the case.

We're told the exact cause of death is still unknown.