Per an official release from Texas Tech:
"I have submitted my resignation to Coach Kingsbury effective immediately because I want the best for the Red Raider program, and this will allow them to go in a different direction on defense," Wallerstedt said. "I love our players and this school and have only their best interest in my heart and mind. I wish Coach Kingsbury every success this season."
"We appreciate all Coach Wallerstedt has done at Texas Tech and we wish him the best," Head Coach Kliff Kingsbury said.
Short and sweet.