This is why sports are so ruthlessly discriminatory. Physical gifts and cultural tendencies lead to pronounced disparities in the racial make up of sports leagues. If members of one group tend to excel at a certain skill, then champions in sports where this skill is essential will tend to come from this group. The huge majority of running backs, wide receivers, base-stealing champions, and sprinters are black. Wiry East Africans dominate distance running, while more muscular folk of West African descent dominate sprinting.
Age discrimination is rampant in sports.
Baseball is unique in the number of players who remain active for 20 years. A pro running back has accomplished something if he stays around for 10 years. If injuries take their toll careers can be cut even shorter. Witness the early exits of Sandy Koufax, Gayle Sayers, Bo Jackson, Bobby Orr, and Bill Walton. Size-ism is a necessary evil in sports.