tax evasion, violation of anti-pollution rules, falsification of tax reports, things like that. iirc he was convicted 6 times, mostly in the '90s. his italian wiki lists all that stuff, it's an unusually long list for someone in his position. he still got the support of most serie a clubs when running for the figc presidency, and despite his uefa ban for racism, when in almost every other european country he should have resigned, he remained in his position.