Excluding 8 vs 9, the most common upset in March Madness is the No. 10 seed over the No. 7 seed in the first round, then the No. 11 seed over the No. 6 seed, and the No. 12 seed over the No. 5 seed. In the second round, it’s the 6 seed vs the 3 seed, then the 7 seed over the 2 seed (excluding 4 vs 5).