The man -- Dale Mooney of Newmarket, New Hampshire -- was rushed to a nearby hospital, where he was pronounced dead. Details surrounding the incident have not been revealed at this time.
The Norfolk District Attorney's Office tells TMZ Sports the investigation is ongoing and is currently in its preliminary stages. No charges have been filed.
Another medical emergency also went down at the same game ... when a second man suffered cardiac arrest earlier in the night.
These are the two heroes from tonight who gave CPR to a fan who went into cardiac arrest at the @Patriots game ❤️ Anthony Colella of Johnston RI Fire and Mark McCullough of Needham Fire pic.twitter.com/qKJ38AKqGw
According to reporter Bridget Condon, two off-duty firefighters sprang into action and conducted CPR for several minutes ... bringing the man back to life. His current status has not been released at this time.