Nor can he leave his post until backup arrives. Instead, he waits for lead base fielder to charge in and then throws to him to begin the standard scheme. During rundown drills in practice, allow all potential ball handlers to play the part of the runner. Have them draw on this experience the next time they're on defense. From the runner's vantage point, they can best sense the optimum moment for the fielder to throw the ball to secure the out.
Baseball offers few occasions where the outcome is certain before a play is over.
But, the next time your defense encounters a rundown, the only unknown may be how to record the out in your score book. All you need is the right strategy and the repetition of practice to make it so.