The initial charge at the start of a sumo bout is called tachiai.
At the tachiai, both wrestlers launch from their crouched starting positions and collide in the center of the dohyo. The impact may be direct, or a wrestler may use timing, a sideways movement, or a defensive tactic instead of meeting the opponent squarely.
Before the charge, wrestlers perform shikiri, the repeated preparation routine in which they crouch, rise, stamp, and throw salt. The tachiai itself begins only when both wrestlers make their simultaneous start.
Tachiai is not simply a test of body weight. Positioning, balance, grip control, speed, and the ability to absorb or redirect force all influence the result. Its rules and timing have also been subjects of debate when starts appear uneven.