There were other factors in the game, but for those downplaying the massive impact pressure on the QB had in the ND / Clemson game; here's a pretty good snippet on the vast differences in Baker Mayfield's season once QB pressure was reduced.
"... 2. Mayfield is getting pressured way less frequently. Owing in part to the tackle change and in part to Mayfield growing more comfortable in the pocket, the Browns have given Mayfield far more time to work with since Kitchens took over. Before the coaching change, Mayfield was pressured on 30.7 percent of his dropbacks, which was the 13th-highest rate among qualifying passers. Since Week 9, though, Mayfield's pressure rate is down to 20.3 percent, which is 31st among 33 passers. Only Drew Brees and Ben Roethlisberger are bothered less frequently. Mayfield has been sacked just once in his past four games. On those rare occasions in which he has been pressured, he has posted an 88.9 Total QBR, up from 16.3 under Haley and Jackson. ..."
Yards are the same but almost every other stat is drastically improved.
SPLIT CMP ATT CMP% YDS Y/ATT TD INT RATING
w/ Haley 130 223 58.3% 1,471 6.6 8 6 78.9
w/ Kitchens 112 153 73.2% 1,406 9.2 11 4 114.4
Link: http://www.espn.com/nfl/story/_/id/25518645/nfl-rookie-quarterback-progress-reports-2018-draft-picks-shown-far
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Link: https://m.youtube.com/watch?v=a01QQZyl-_I
No question, that Desmond Harrison was simply not ready to play at the NFL level. The Browns coaching staff was rather short-sighted for thinking that he was the right guy to replace the retired Joe Thomas.
His (Harrison's) numbers looked amazing from a sheer athletic point of view, but he never showed that he could at least play against the best at the FBS level, much less the NFL He's been beaten pretty badly by some mediocre defensive ends throughout the year, and when your left tackle (who is supposed to be your best pass blocker) can't do the job, it's a no-brainer that your QB is going to get pressured.
Besides, the off-the-field issues, he was simply a big fish in a little pond, where he was able to out-muscle a bunch of weaklings while playing at West Georgia. Unfortunately for him, once he got to the NFL, even the smaller defensive ends were running over him with sheer physical strength, and after he got shell shocked by that, it was easy for them to run around him.