Assuming this is limited to athletes, not coaches.
Football: Dan Orlovsky-brought us recognition that most thought would take 10 years.
Basketball: Khalid el Amin. We don’t win title #1 without his cocky yet intense personality. Got us over the almost but not quite good enough hump. After him UConn’s image changed.
Womens basketball: Rebecca Lobo. Another case of someone who led the program to its first title and set the standard for those who came after.
Hockey: Hudson Schandor. Didn’t get us to the Frozen Four but did to the NCAAs for the first time. Another guy who set a standard that future players will need to live up to.
Soccer: Joe Morrone, Jr. Won the soccer equivalent of the Heisman, the Hermann Trophy. All-American, Selected for the 1980 Olympics, scored the winning goal to qualify Team USA for the Games (USA ultimately boycotted Moscow games over Soviet invasion of Afghanistan).
Baseball: Charles Nagy. Great college career. Went on to be a 3 time All Star and is in the Cleveland Guardians Hall of Fame.