Softball 4 life,
Those are all good questions. I'll try to offer some good answers!
1) Hard to tell what's going through a runner's head as she rounds third at blazing speed, fueled by excitement and adrenaline, intent on scoring that run.
Players often do things in the heat of the moment that aren't "logical" or the "best choice".
Stopping and heading back to third is an option. Another option would be to execute a "slide-by" or "backdoor" slide to get around the catcher.
Whichever choice the runner makes, the rules say that they cannot remain on their feet and crash into the catcher.
2) My daughter was also a catcher through most of her playing days. Here are some of the things I taught her and that we picked-up in catching clinics.
Especially with the recent rule changes on obstruction, the catcher should not be setting-up "on top of the plate". The rules state that the catcher cannot block the plate without the ball.
Instead, set-up just in front of the plate. After receiving the ball, do your drop back into the basepath. Once you have the ball, you may legally block the base. You can also execute a swipe tag on the runner.
By the obstruction rule, you must allow the runner access to ALL of the plate, not just a portion of it. The runner is free to take any basepath she chooses to reach the plate (or any other base).
Blocking the base without the ball leaves the catcher open to an obstruction call. However, even if the catcher is blocking without the ball, it DOES NOT relieve the base runner from he responsibility to either slide or avoid contact. It does not give the runner free rein to mow down the catcher.
An interference call on the runner takes presedence over an obstruction call on the catcher. Umpires that know what they're doing will make this call.
Bottom line- if the catcher does not have the ball, they should not be blocking the base. Move out of the way of the runner if you do not have the ball!
3) The umpire must use all of his experience and rules knowledge to make these calls the right way. It is a tough call to make, since the play is usually "bang-bang" and has to be made in an instant.
Some things the umpire can look for:
Did the runner alter her path to make contact with the catcher?
Did the runner slow before making contact?
Did the runner lower a shoulder or throw an elbow before making contact?
There a basically four levels of contact that can be made on this play.
A runner can legally slide and make contact with the catcher. There is no penalty for contact made while executing a legal slide.
A runner might make incidental contact on a play, with the two players barely brushing against each other, or with the runner making a quick move away from the catcher at the last instant. That would be "nothing" and no penalty would be enforced.
A runner might simply remain on her feet and, without altering her path or doing anything malicious, and crash into the catcher. The runner should be called "out" for doing this.
A runner might remain on her feet and crash the catcher with great force, with the intent of dislodging the ball. If she does any of the things mentioned above (lower a shoulder, throw an elbow or alter her path to make the contact) the runner is "out" and an ejection is warranted.
It takes an experienced official to sort out which of these happened in the split second that this play unfolds.
3.5) Yes, there is umpire judgement involved. But, most of the judgement involves the intensity of the crash and the intent of the runner.
What is protestable is a rule interpretation. For instance, if a runner crashes into the catcher and is not called out, the umpire has not properly interpreted a rule. That is grounds for a protest. The rules specifically call this an infraction and give a specific penalty.
Plays at home should be governed by two simple principles. If the catcher does not have the ball get out of the way, and that runners must either slide or avoid contact on every play.