I believe that Troy refused to accept that things had changed for African Americans in professional sports and while racism was still prevalent, Cory would not face as many obstacles as Troy did.
A part of me felt that Troy envied the possibility of his son making it farther than he did in sports and this and the fact and his outright refusal to hear the others that things were different fueled him to refuse to sign the papers.
His justification for his actions was that he was trying to protect Cory even when everyone else was telling him he didn't need protecting.
In the end he loses his son in the process.
What do you guys think?