Complex sentence: Theodore Long then vacated the title and announced that the two would face off against one another in a "Best of Seven series" for the title, in which the winner would be the man who wins four matches over the other first.
Split into simpler sentences: Theodore Long then vacated the title and announced that the two would face off against one another in a "Best of Seven series" for the title. In a "Best of Seven series", the winner is the man who wins four matches over the other first.