Why do sumo wrestlers throw salt in the ring?

Salt is believed to have purifying powers, so it supposedly makes the ring a sacred place.

https://www.youtube.com/watch?v=BtU3MsJfG4U

It's a purification ritual of the Japanese religion, Shinto. Shubatsu is a purification ritual in which salt is sprinkled on priests or worshippers, or on the ground to purify it. One notable use of salt in purification is found in Sumo wrestling when the fighters sprinkle salt around the ring to purify it.
https://en.wikipedia.org/wiki/Harae

Use of Salt in ritual purification is a world-wide practice:
Salt -- whether common table salt, sea salt, or kosher salt -- has a long history of use in rituals of purification, magical protection, and blessing. Among spell-casters working in the European folk-magic tradition, it is a commonplace to lay down a pinch of salt in each corner of a room before performing a spell. This has carried over into contemporary African-American hoodoo practice as well.
http://www.luckymojo.com/salt.html

Salt, as in ordinary household salt, is a powerful absorber of psychic energy. It doesn't channel this energy but absorbs it and holds it instead and it is this central property which accounts for its many different uses in magic. Here is a list of magic uses for salt plus some easy salt spells for clearing, protection and purification.

http://magic-spells-and-potions.com/magical_properties_of_salt_protection_purification_healing.htm