One throw and get an out and you don't have to worry about who gets involved. I tell my guys all the time if we make more than two throws then just stop and let them have the base because we messed it up. When it comes to a rundown you have to get the runner committed in a direction. Then either run him down for the tag or close the gap and short toss to the receiving player. Make sure you are slightly inside the runner so the one chasing can just reach out and tag plus the receiver will be catching with his glove at the runner. If the runner isn't committed to going in a direction then you're going to make a lot of throws. Make them commit, throw and get the tag while they are taking several steps to stop and change directions.