Spider Sabich
Hank Gathers, Loyola Marymount University, Southern California, 1990. Was playing against Portland during a WCC tournament game, had a dunk midway through the first half, started down court, collapsed, and was declared DOA at the hospital, at the age of 23. (hypertrophic cardiomyopathy)
LMU players rallied and made it to the Elite 8 that year, losing to eventual champ UNLV.
Note: star guard Bo Kimble began a tribute to Gathers that would continue through the tournament, and into his playing career - Kimble would shoot his first free-throw left handed (Gathers was right-handed, but a poor free thrower and had started trying to shoot with his left hand) before going back to his natural right handed shooting.