How to Tell When a College Basketball Game is Out of Reach: Take the number of points one team is ahead. Subtract three. Add a half-point if the team that is ahead has the ball, and subtract a half-point if the other team has the ball. (Numbers less than zero become zero.) Square that. If the result is greater than the number of seconds left in the game, the lead is safe.
Or you could just use the handy Bill James Lead Calculator.