According to Pete Roussel, Texas Tech defensive coordinator has been dismissed from the coaching staff.

Breaking: Texas Tech DC Matt Wallerstedt has been dismissed from the staff. Details coming on http://t.co/VP1ldkYydJ

— Pete Roussel (@coachingsearch) September 18, 2025

I'll update this post as needed.

UPDATE 1: According to Chris Level, Mike Smith will be taking over defensive coordinator duties:

Matt Wallerstedt out as #TexasTech's DC. Mike Smith will take the reigns now.

— Chris Level (@ChrisLevel) September 18, 2025

UPDATE 2: According to ESPN:

Texas Tech fired defensive coordinator Matt Wallerstedt on Thursday after the coach was suspected of being at the school's football building while under the influence of a controlled substance, sources told ESPN.com.

UPDATE 3: ESPN has updated their story to now say that it was an "unknown" substance rather than a "controlled" substance.