Position: A third base coach who realizes when a ball is going to beat the runner by, say, 15 feet, you don't send him.
Must:
Have full sight.
Be able to swing arm in windmill motion.
Willing to wear plastic helmet.
Common sense.
Should:
Speak Spanish.
Have hands.
Not necessary:
Hold prior coaching job...ever. As long as you understand baseball more than Luis Aguayo.