Players notify stadium security when a fan, reaching for a foul ball, drops and then retrieves a gun on the field at Comerica Park. It turns out to be a Glock pistol belonging to an embarrassed off-duty three-year veteran of the Detroit Police Department, who had his weapon fall out of its holster as he went for the ball.

On July 18, 2001 — Players notify stadium security when a fan, reaching for a foul ball, drops and then retrieves a gun on the field at Comerica Park. It turns out to be a Glock pistol belonging to an embarrassed off-duty three-year veteran of the Detroit Police Department, who had his weapon fall out of its holster as he went for the ball.

Source:
Baseball Reference July 18