No, it's legal to go back head first.
Yes. You cannot slide head first while advancing but you can dive head first BACK to a base.
If they are holding on to their gloves they cannot dive palms down and road rash them, also outstretched fingers often get jammed on the base or cleated by the short stop. In the event they have to slide into the base, they stand the chance of ruining the gloves given they slide into the base using their hands. They slide head first and the gloves are expensive. I heard that some also do that to remind them not to slide head-first.
Yes. There is no MLB rule that prohibits sliding or diving head first into any base.
No, in Major League Baseball a base runner can slide into any base in any direction.
Yes . But why?
You can slide into 1st base. Generally, it is not recommended. There are two scenarios where you may want to slide into first. 1) You have hit the ball and are running toward first. The first baseman is positioning to receive the throw. You can see that the throw is offline and the defender may try to tag you instead of touching the base, or the throw has put the defender in your basepath. You slide to avoid a tag or the defender. 2) You have a base hit and have rounded the bag. A throw is coming toward 1st base and you need to return. You may want to slide back to the bag to avoid the tag while off the base.
Yes.
Pete Rose?
The body falls to the ground in a controlled manner by a fall backward on the outer surface of the knee and lower leg, or just by diving head first.
Yes, a runner may slide into any base at any time.
It happens, but not very often.