Deals for third-tier rights vary by conference. Some third-tier rights are bundled by conferences and sold to regional networks while others are retained by schools and sold individually to local or regional networks. For example, Pac-12 schools have pledged their third-tier rights to the upcoming Pac-12 Network. Scott Farmer signed over the UL third-tier rights to the Sun Belt Conference to bundle without approval.
I'm not sure I can explain it any better then this without a copy of the SBC television contract.