Why do Sumo wrestlers stomp on the mat before each match?

Answer 1

they hit their selves to show they are strong and to get mad

Answer 2

It is a part of the purification process. They are actually spreading salt, some place it in their mouths, others slap it on their chests.

Answer 3

To drive evil spirits away from the dohyo (the ring).

Answer 4

To ward off evil spirits.