Texas Tech DC Wallerstedt resigns, suspected of coaching under the influence of unknown substance

Former Texas Tech defensive coordinator Matt Wallerstedt has resigned amid suspicions he was coaching under the influence.

"I have submitted my resignation to Coach (Kliff) 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. 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."

Wallerstedt is expected to be replaced by co-defensive coordinator and linebackers coach Mike Smith, ESPN's Jake Trotter said Thursday. Smith is a former Red Raider who graduated from Texas Tech in 2004.

"We appreciate all Coach Wallerstedt has done at Texas Tech and we wish him the best," Kingsbury added as part of the statement.

Wallerstedt was sent home from Texas Tech's football facility Monday, according to Trotter.