Does anyone know who has won national and World titles by defeating the reigning champ? How often has this happened?
It happens all the time.
Worlds
Ladies:
27 Sonja Henie defeated champ Herma Szabo
38 Megan Taylor defeated champ Cecelia Colledge
54 Ghundi Busch defeated champ Tenley Albright
56 Carol Heiss defeated champ Tenley Albright
66 Peggy Fleming defeated champ Petra bruke
75 Dianne de Leeuw defeated champ Christine Erath
76 Dorothy Hamil defeated champ Dianne de Leeuw
78 Anette Petzch defeated champ Linda Franianne
79 Linda Franianne defeated champ Anette Petzch
80 Anette Petzch defeated champ Linda Franianne
86 Debi Thomas defeated champ Kat Witt
87 Kat Witt defeated champ Debi Thomas
90 Jill Treneary defeated champ Midori Ito
96 Michelle Kwan defeated champ Chen Lu
97 Tara lipinski defeated champ Michelle Kwan
99 Maria Buturskya defeated champ Michelle Kwan
00 Michelle Kwan defeated champ Maria Buturskya
02 Irina Slutskya defeated champ Michelle Kwan
That's just a sampler.
I think that Roz Sumners defeated reigning National and World Champ Elayne Zayak.
Elaine withdrew from 83 worlds with injury. I don't consider that a "defeat". Roz did defeat Elaine at 82 nats, where Elaine took bronze.