one other question....... 2 runners cannot occupy the same base at the same time BUT...... if does happen, is the lead runner automaticaly out or does a defender have to make a tag?
There's no automatic out on this play. The defense has to make a tag to get the out.
Depending on the game situation, it's not always the lead runner who is subject to being tagged out. When two runners are on the same base, the lead runner is out on a tag IF the lead runner is forced to advance (ie: by definition of a force play, forced to advance by the batter becoming a batter-runner).
If the lead runner was not forced to advance, then the trailing runner is the one liable to be tagged out.
There is one way a play like this can result in an out being called without a tag and I guess you could call that an "automatic" out. Suppose that two runners were on one base and the defense didn't tag either one of them! They just threw the ball back to the pitcher and she prepared to make the next pitch.
The umpire is supposed to wait long enough that it's obvious no play is going to be made on the runners and the runners aren't trying to advance or retreat, then call time, then declare out the runner who is not entitled to be on the base. I've never had it get to that point before. The defense has always made a tag on this play- and, often, they will tag both runners "just to be sure"!