The Milwaukee Bucks were in the midst of a comeback on Tuesday against the Atlanta Hawks, who were without their best player, Trae Young. With the Bucks up by two games to one in the best-of-seven Eastern Conference finals series, a win would have put the franchise on the brink of making its first N.B.A. finals since 1974.
Then a nightmare unfolded in the third quarter: The Bucks’ star and one of the league’s best players, Giannis Antetokounmpo, landed awkwardly while trying to defend an alley-oop dunk and crumpled to the ground, holding his left knee and writhing in pain.