He was 74. No cause of death was announced.
Bellamy was an All-American at Indiana and won a gold medal in the 1960 Olympics before being made the No. 1 overall pick in the 1961 draft by the Chicago Packers.
Bellamy averaged 31.6 points and 19 rebounds for the Packers in 1961-62, making the All-Star team and earning the Rookie of the Year award.
He averaged 20.1 points and 13.7 rebounds in 14 seasons with the Packers, Baltimore Bullets, New York Knicks, Detroit Pistons, Hawks and New Orleans Jazz. He retired in 1975 and was inducted into the Basketball Hall of Fame in 1993.
"The Atlanta Hawks family is saddened to learn of the death of Walt Bellamy at the age of 74 earlier today," the team said in a statement. "The Hawks and the National Basketball Association have lost a giant. As an Olympic gold medalist, the first overall pick in 1961, Rookie of the Year in 1962, a four-time All-Star and a member of the Naismith Memorial Basketball Hall of Fame, his on-court accomplishments were overwhelming. Off the court, he was equally impactful as a family man, leader in the community, mentor and friend to many."
Orlando Magic forward Tobias Harris is still weeks away from returning to the court because of a severely sprained ankle he sustained two weeks ago during the preseason, the team said Saturday.
Acquired from the Milwaukee Bucks during last season, Harris averaged 17.3 points, 8.5 rebounds, 2.1 assists, 0.9 steals, 1.4 blocks and 36 minutes over 27 games with Orlando.
Brooklyn Nets center-forward Andray Blatche was fined $15,000 for making an obscene gesture during the Nets' 101-100 win over the Heat on Friday, the NBA announced.
Blatche made the gesture with 2:40 left in the fourth quarter.
He had nine points and six rebounds in 25 minutes.
Minnesota Timberwolves reserve center Ronny Turiaf underwent an MRI on Saturday that revealed a radial head fracture of the right elbow.
The Timberwolves will re-evaluate Turiaf next week to determine an approximate timetable for his return.
Turiaf was injured with 10:17 left in the second quarter of Friday's win over the Oklahoma City Thunder.
He played just three minutes.