Some scientists caution that much remains unknown about C.T.E., including why it afflicts some players but not others. But even the N.F.L., which for years denied there was any connection between head trauma sustained on the field and long-term cognitive impairment, has admitted that there is a link.

Smith, whose given name was Charles, died at age 66 of an overdose of phentermine, a weight-loss drug. He also had heart disease and high blood pressure, according to the Los Angeles County coroner.

At 6 feet 7 inches and nearly 300 pounds, Smith was known as a quick and powerful lineman. During a standout career at Michigan State, where he was named an all-American in 1965 and 1966, Smith’s size and prowess gave rise to the chant “Kill, Bubba, Kill,” which emanated frequently from the stands. (He later co-wrote a book with that title.)

Smith was chosen as the No. 1 overall pick in the 1967 draft by the Baltimore Colts. He was a member of the teams that lost Super Bowl III to the Jets and beat the Dallas Cowboys in Super Bowl V. After five seasons in Baltimore, Smith played two seasons with the Oakland Raiders and two seasons in Houston with the Oilers.