Texas Tech DC Matt Wallerstedt resigns for ‘personal reasons’

Texas Tech defensive coordinator Matt Wallerstedt has resigned for "personal reasons," the team announced Thursday. 

"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 in the release. "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."

Sources indicated to FOX Sports Southwest that Wallerstedt’s exit, widely reported earlier in the day, was for reasons outside of his on-field performance. 

ESPN.com reported Thursday that Wallerstedt was sent home from the team facility on Monday and was suspected of being under the influence of an "unknown" substance.

"We appreciate all Coach Wallerstedt has done at Texas Tech and we wish him the best," Kingsbury said in the release. 

Co-defensive coordinator Mike Smith will take over Wallerstedt’s duties. The Red Raiders promoted defensive quality control assistant Matt Brock to inside linebackers coach. 

Smith will be Texas Tech’s sixth defensive coordinator in the past six seasons and seventh since 2007.