I can find no evidence on any major recruiting site that Clemson offered him, and Rivals is the only one that even mentioned a Clemson interest. How do you know this?
I did find this Jeremy Pernell article excerpt below, but this is a far cry from saying Clemson was seriously interested:
A month later, on February 29, he (Haarberg) had a good showing at an Elite 11 Regional held in Atlanta. As spring unfolded, Haarberg saw his profile rise and along with the Huskers, began hearing regularly from coaches at Clemson, Auburn, Oregon, Cockeye, Northwestern, Boston College, Duke, Kansas State, NC State, Utah and Vanderbilt. In fact, Kearney Catholic head coach Rashawn Harvey revealed that roughly 15 colleges had plans to stop by the school before the NCAA instituted a recruiting dead period in response to the coronavirus pandemic.
The cancellation of the spring evaluation period probably cost Haarberg a number of Power Five offers. By the first week of April, he had offers from Wyoming, Buffalo, Central Michigan, Northern Illinois and a few other FCS and Ivy League schools. Had he gotten the opportunity to throw in front of coaches while showing off his size and athleticism, it’s not hard to imagine he would have become quite popular. Despite the circumstances, Haarberg received his first major offer from Boston College on April 8. Three days later, Costelli disappointed Husker coaches and chose Utah.
Frost and Verduzco had long expressed their preference to see Haarberg throw at one of their Friday Night Lights camps planned for June. In mid-April, however, it was unknown whether camps would be allowed since the NCAA was incrementally extending the dead period. Nebraska was in a bind. On one hand, they clearly liked what they saw of Haarberg on film. But they have a process they trust and were hesitant to deviate from that. With their board shrinking, Frost and Verduzco came to realize seeing him throw was unlikely. They also knew Haarberg was continuing to gain notoriety nationally. Roughly three weeks later, on May 4, they decided to extend an offer. The same day, Haarberg received offers from NC State and Vanderbilt.
Heinrich didn’t take long to accept the offer, committing to the Huskers on May 9 over fellow finalist Boston College.
