an excited exclamation by the late Myron Cope, color commentator for the Pittsburgh Stillers (Steelers). Often yelled with a single "YOI!" when a great play or great hit occured on the field.
Bill Hillgrove: "Wow, look at the hit Polamalu put on the reciever"
Myron Cope: "Yoi!, and Double Yoi! dat Polamalu can cover da whole field"