Each regional has 4 teams seeded 1-4. The 1 seeds host. These 1 seeds are all seeded 1-16. This is called the national seeds.
Anyway, since there are 16 regional sites, there are 16 regional 1 seeds, 16 2s, 16 3s, and 16 4s.
TCU was a 2-seed in the Stillwater regional. They won it. So they advanced to play in the Super Regional.
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Seeding doesn't matter in the Supers, besides the higher seed hosting. But it's the winner of a regional vs the winner of another regional.
Once we have 8 super winners, they go to Omaha.
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It's a double-elimination bracket. The teams are placed like a normal 2nd round matchup 1-16 winner, 8-9 winner, etc like a basketball bracket. But that's from the host seedings of the regionals, not re-seeding the teams that are still alive.