It is only the "smart" thing to do..
Assuming the catcher is near home plate, the runner has to slide. If he doesn't and knocks the catcher down he is out. If the catcher is up the baseline and is waiting to make the tag the runner would be called out for crashing into him. If the slide knocks the catcher down, the outcome of the play would depend on whether the catcher maintained control of the ball during the tag and whether the runner touched home plate.
No they dont if they dont wont to
Whenever there is a play the runner has to slide. there is no mandatory slide rule the runner just has to avoid contact
There are two situations. (1) If the catcher (or any defensive player) has possession of the ball the runner (Rule 7.08(a)(2) the runner is out if "the runner does not slide or attempt to get around a fielder who has the ball and is waiting to make the tag." In addition, if the umpire judges that the runner was malicious and trying to injure the fielder (including the catcher) the umpire may eject the player. However, if the catcher does NOT have possession of the ball and therefore is not waiting to make the tag, the catcher is guilty of obstruction (Rule 2.00, definition of obstruction). If the umpire makes this judgement, the runner would be awarded the base to the runner. This does not give the runner free license to slam into the catcher. Again, if the umpire judges the runner was malicious, the runner would be awarded the base (including scoring the run) and then the umpire may eject the player. In addition, if the umpire judges that the catcher was malicious and was malicious in their action (causing injury to the runner), the catcher may be ejected. So the bottom line is that the runner and catcher are expected to avoid malicious contact.
No. That would be an obstruction and the base-runner would be safe.
This rule states that if a defensive player does not have the ball, she cannot stop the runner from reaching the next base. She could stop the player by standing in her way, or putting her leg down to block a slide before she has the ball to tag her out. A catcher can also block the plate by not allowing the runner a clear path to the plate when they do not have the ball. If a player does have the ball, they are allowed to block the bases though.
Depending on your league rules. In general, the answer is yes, provided that your league has not adopted a "must slide rule".
Yes. If at any point in a game, the batter or baserunner interferes with the fielder, he is an automatic out. If he impedes the throw to get out another runner, the other runner is out as well. For instance, on a double play, if the runner going to second is already out by force at 2nd, and he plows into the short stop trying to throw the other runner out at first, the runner going to first is also out. The baserunner must always slide or otherwise avoid excessive contact with the fielder on a double play.
A runner can slide into any base.
If you are unsure that you will make it in time before the catcher gets the ball and tags you. But if you are certain, you can just run over if. But as long as you touch the plate before, your safe.
Yes, a runner may slide into any base at any time.