v. phr. 1. To watch the ball at all times in a sport, usually in order to hit it or get it; not stop watching the ball. Keep your eye on the baseball or you won't be able to hit it. 2. informal To be watchful and ready; be wide-awake and ready to win or succeed; be smart. Tom is just starting on the job but if he keeps his eye on the ball, he will be promoted.
Compare: ON THE BALL, KEEP AN EYE ON or KEEP ONE'S EYE ON or HAVE ONE'S EYE ON.