Obviously a penalty and late hit. Player was ejected for it, and will probably be fined and maybe suspended.
If the NFL doesn't have this rule where you can't hit a QB after he begins his slide, this doesn't happen. Lawrence would have instead protected himself instead of leaving himself vulnerable hoping the defensive players will follow the rules and not misjudge.
If a QB fakes a slide, then defenders will hesitate to hit him, not wanting to risk a fine and suspension. Then the QB continues to run for another 20 yards. So then defenders will just think you know what we want to win these games so might as well just hit the motherf*****.
Hitting the QB is an age-old strategy to keep them rattled. It will never go away. Defensive players do not want to miss an opportunity to rattle a QB, which likely leads to situations like the Lawrence hit, where they misjudge or simply think it's worth it to commit the foul. After all, it probably did help the Texans win.
Some of you may think it's not that complicated. That the guy just chose to make a dirty hit and deserves to be suspended for a year and fined hundreds of thousands of dollars or whatever to set a precedent. That's a fair opinion, too, but I like to think about the nuances and complexities of such situations and how it relates to the game itself.