The world championship match between Viswanathan Anand and Veselin Topalov is nearing the end of its scheduled series of games, and the score is currently tied with one game left.
In previous world championships that I am aware of, in this situation, the match would have been declared a tie and the current champion (Anand) would simply retain his title.
But in this match, there is a tie-breaker format defined, in which the players will play a series of faster games, with much stricter time controls, culminating in an "Armageddon game" if the match remains tied after those short games are played.
I clearly hadn't been paying enough attention before, for I wasn't aware of these tie-breaker rules. It's nice to have a clear victor, but as in many sporting situations, the tie breakers are unsatisfying in many respects.
Perhaps there will be a clear victor in the final match today.
Update: The game is a fierce fight! Anand has conducted a tremendous attack and has won Topalov's queen. The game has been underway for many hours and still is not resolved.
Update 2: It's over, Topalov resigned. Mate was imminent (the immediate thread was Qh1 mate).