Lexington Catholic as a #4 seed in 1997 when they went on the road to #1 seed Rockcastle Co. for a win in the playoffs and then went to Danville to beat Danville in round 2 of the playoffs on the last play of the game. I believe those two wins on the road were the type of upsets that got the program where it felt it could compete with anyone. They went on to have some other great upsets, such as, Boyle Co. in 1998 & 2004, St. X. in 2003, Male in 2001, Riussle in 2000 playoffs when they were the #1 seed, Beechwood in the mid 90's, and Henry Clay in 1996, and of course Highlands at Highlands this year. Those are just some of their wins as they climbed the ladder over the past 15 years. You pick the biggest upset of the bunch.
Speaking of those upsets over those 15 years, I was listening to a documentary of John Wooden's career at UCLA and I noticed that it was his 15th year when they won their first title and his program wasn't starting from scratch. Funny how some think it took Lexington Catholic a long time to win one. Of course, those are the same people who complained that UCLA had an unfair advantage of some kind.