Let's say, for example, that Joe and Bob are in a formal debate over whether the products used to clean stoves are safe. Joe starts the debate by arguing that the products are unsafe. He cites a few pieces of evidence that are anecdotal and are therefore likely to be disregarded by the judges. Joe bases most or all of his argument on this evidence. However, at no point does Joe offer evidence that serves to refute his argument.
So, essentially, it would be safe to say Bob has basically won the debate before he said anything.