The Texans had four defensive linemen hitting free agency this year. Joel Heath, Brandon Dunn, Angelo Blackson, and Christian Covington. The Texans extended a qualifying offer to Dunn, and resigned Blackson and Heath. Covington ended up being the odd man out. He signed a one-year contract to remain in Texas and play for the Dallas Cowboys.
Covington had one decent game as a pass rusher in 2018. Like the rest of the bunch, he's fine against the run, but can't muster a rush on his own.