You can look up the history of the ACCs "800 Rule" and find several articles on it and South Carolina leaving. Here's a portion of one:
"From Simmer to Boil
By 1970, the situation between USC and its ACC brethren reached a boiling point. After winning the ACC title in 1969, Dietzel’s in-state recruiting had taken off. But of the ten “blue chip” in-state players Dietzel eyed, only two had managed the requisite score of 800 on the SAT. Beyond the 1970 recruiting class, Sumter wide-receiver Freddie Solomon promised to be the most celebrated recruit of Dietzel’s tenure in 1971, though the ACC’s 800 standard remained a serious roadblock. Dietzel vented his frustrations to President Jones, lamenting that he was tired of watching high school players from South Carolina go onto all-American careers at Big Ten and Big Eight schools, only because they were barred from competition within the ACC by the onerous 800-rule.
(Solomon did not score the requisite 800 on his SAT and went on to star at the University of Tampa, from there playing eleven years for the Dolphins and 49ers of the NFL. In the 1982 NFC Championship game, made famous by “The Catch” – Dwight Clark’s iconic leaping touchdown grab, Solomon was the primary target on the play. Quarterback Joe Montana checked off to Clark when Solomon slipped on his route. Solomon figured prominently for the 49ers on the final and deciding drive of that game.)
The NCAA expressed support for Dietzel’s stance, noting that it was against the ACC’s use of a minimum cutoff score. Further, the 800-rule had caught the attention of the federal government, which was investigating colleges and universities across the South for prejudicial admissions standards.
On October 21, 1970, amid continuing acrimony between member institutions over the 800-rule, ACC presidents met to discuss the matter. They ultimately opted to pursue additional studies on the effects of dropping the rule in favor of another predictive model. Two days later, the University of South Carolina’s Board of Trustees took the matter into their own hands, authorizing Gamecock coaches to recruit on the basis of the NCAA’s 1.6 standard. While they pledged that the University would continue to work toward a solution with the ACC, it was a brazen act of institutional defiance.
South Carolina had thrown down the proverbial gauntlet, which forced Clemson into the position of choosing a course of action. Though Clemson’s Edwards and Howard shared Carolina’s stance on the 800-controversy, they were less inclined to bolt the ACC. Despite a popular misconception among Carolina faithful, there was never a “pact” between USC and Clemson officials to leave the conference together. Clemson ultimately chose to remain in the conference, while South Carolina charted its own course. On March 28, 1971 the Board of Trustees announced the university would withdraw from the conference on August 15 of that year.
In a statement read by Board of Trustees Chairman, T. Eston Marchant following a daylong meeting to discuss the matter, the Board sounded an optimistic tone. Marchant cited national legislation then under review, which would “remove the areas of disagreement which presently exist (between USC and the ACC).” The statement went on to express hopes that the separation would be of a “temporary nature.” Newly elected ACC Commissioner Bob James attended a portion of the meeting and expressed similar optimism for reconciliation after returning to his home in Greensboro, N.C. “I was really impressed with the sincerity of the South Carolina people. I came away with the feeling that they want and would like to be in the ACC.”
The measured optimism of USC’s Board and the ACC’s new commissioner were balanced by comments from other officials who sounded a tone of resignation, bordering on indifference. Maryland Athletic Director Jim Kehoe, in addressing the scheduling difficulties presented by South Carolina’s withdrawal, noted that “It would seem to be more sensible to compete with teams 150 miles away than one 300 miles away.” He added, “I’m sorry the matter couldn’t be resolved, but realistically, South Carolina had gone too far down the road to remain in the conference.”
And so, just over two weeks after that glorious day in Greensboro, the University of South Carolina officially announced a parting of the ways with the Atlantic Coast Conference, only hours before the basketball team would meet for their annual post-season banquet to celebrate their first ACC basketball championship.
The 800-rule controversy was resolved shortly after USC’s exit when two students at Clemson University filed suit in federal court against Clemson and the ACC. Their attorneys argued that the 800-rule deprived them of their Constitutional rights under the 14th amendment since the rule applied only to athletes. On August 7, 1971, a federal court ruled that the ACC’s 800 standard was “arbitrary and capricious,” and was “not based on valid reasoning,” as it set a standard for athletes which did not apply to other students. On August 18, 1971, just three days after the University of South Carolina officially relinquished its membership, the ACC dropped the embattled 800-rule."
And the whole article:
https://southcarolina.rivals.com/news/storms-in-the-southland-from-simmer-to-boil