Based on fight. Just my speculation based on those who were more aggressive. Mitch Matthews basically confirmed this when he talked about the team being down a safety and lb, while also stating others will have to step up.
Rumor also floating around that a couple more suspensions based on off the field bowl activity. There is also usually a couple who are held out of fall camp or games for academics as well. Pikula and Langi were two who reportedly had issues in spring so hopefully they hit the books.
In other words, our defense will likely be down several guys.