Matta: False Start
Matta (待った) is a stopped start in sumo. It is called when the wrestlers do not begin through proper mutual readiness, including cases where a wrestler launches before the other is set.
When a matta is called, the wrestlers return to their corners, recompose themselves, and restart the pre-bout ritual. A wrestler who commits multiple false starts in a tournament may receive a warning from officials.
The tachiai is self-timed by the wrestlers rather than started by a whistle. The gyoji watches their readiness and can stop an improper opening. This is why a matta may be called even when the first movement looked quick enough to be a normal charge.