In professional Japanese sumo when a sumo wrestler is kadoban wo mukaeru - facing kadoban - it means that he is an ozeki (Champion) who is facing demotion, unless he pulls himself together and secures enough wins to avoid it. In a basho that lasts 15 days this means winning at least 8 bouts, since promotion and demotion depends on the sumotori winning or losing more than half of the bouts in the basho.
For all other sumotori the rule is that kachikoshi (more wins than losses) means promotion, and makekoshi (more losses than wins) means demotion. For the ozeki (and the yokozuna1), though, the rules are different:
An ozeki is allowed to get makekoshi in one basho without being demoted. In the following basho he is kadoban, and must secure a kachikoshi or be demoted to the highest sekiwake position.
- The yokozuna (Grand Champion) cannot be demoted, but is expected to retire if he begins to perform poorly.
My sources are Sumoforum.net and countless hours of watching sumo.