In short, some of the worst defense in school history.
Ohio State will enter the Rose Bowl allowing 25.7 points per game and 400.3 yards per game, both higher than the school record entering the season. (The Buckeyes allowed 24.7 points per game in 1989 and 385.7 yards per game in 1988.)
Football Outsiders again offers a strong indication: While the Buckeyes have been above average on a play-by-play basis (35th in success rate), only six teams were worse at preventing explosive plays (124th in IsoPPP+).
The Buckeyes had no bread-and-butter on defense, neither strong against the run (61st nationally in yards allowed per game and 79th in rushing S&P+) or pass (83rd in yards per game and 74th in passing S&P+).
Although Ohio State ended the regular season second in the Big Ten in sacks, the pass rush was inconsistent for much of the year — especially early on.
How did that happen?
Bosa’s season-ending core muscle injury in week three against TCU was a big factor.
He had been a one-man wrecking crew up to that point, making enough plays to cover up for a lot of shortcomings the rest of the unit might have.
Multiple talented players were left in his wake, but junior tackles Robert Landers and Dre’Mont Jones were both banged up for much of the year, too, leaving the unit as a whole not as dominant as it was expected to be. Davon Hamilton was solid backing up Landers but a handful of youngsters were more down than up when filling in for Jones.
Injuries and inexperience have hindered Ohio State?s defensive line this season, but they might be rounding into form just in time.
Defensive end Chase Young appeared to break out with three tackles for loss at Penn State on Sept. 29, but he had only 2.5 stops in the backfield over the next five games. On the bright side, he flipped the switch back on for the last three games, tallying six TFLs against Maryland, Michigan and Northwestern.
The defensive line failing to be the strength it was expected to be put more of an onus on the linebackers to be difference-makers, something they seemed ill-suited for.
Frequently caught up in the wash when they weren’t simply out of their gaps, the linebackers disappeared too often throughout the season.
Malik Harrison, whose play perhaps not surprisingly seemed to improve as the defensive line got healthier in November, led the team with 74 total tackles, including a combined 17 in wins over Michigan and Northwestern.
Tuf Borland, a sophomore who began the year still slowed by an Achilles injury, proved to be strong against power teams such as Michigan and Michigan State but was less effective against spread teams. The staff had him splitting time with highly regarded sophomore Baron Browning early in the season, but Browning was inconsistent when given opportunities.
Pete Werner, another sophomore, was frequently asked to play in space and held his own, though he was often fighting an uphill battle. He made one of the biggest plays of the season when he broke up a potential touchdown pass against Michigan when the game was still in doubt.
Linebacker Pete Werner describes a strategy that gave the Buckeyes a problem against Minnesota: run-pass options.
Whatever the struggles of the linebackers, the secondary was worse.
The cornerbacks were often victimized in man coverage while the safeties frequently failed to adequately provide a last line of defense.
Damon Arnette, Kendall Sheffield and Jeffrey Okudah were all about as likely to be called for pass interference or give up a long catch as they were to break up a pass, something that continued from the beginning of the season to the end.
Redshirt freshman Shaun Wade showed some promise at safety late in the season but struggled in man coverage as the team’s nickel cornerback.
Despite missing the season opener with an injury, junior safety Jordan Fuller (a returning starter) led the secondary with 72 tackles, but he wasn't able to clean up the messes left by everyone else as much as necessary.
Sophomore Brendan White provided a lift late in the season, logging 13 tackles against Nebraska but also being among those who were flummoxed by Maryland's offense when the Terrapins put an astounding 535 yards and 44 points on the Buckeyes.
If youth, inexperience and injuries were a big part of the defense’s problems in 2018, there’s good news: Injuries are always going to be part of the game, but the Buckeyes should be older and wiser in 2019.
Although Bosa is not coming back and Jones is a good bet to leave, too, Young could be in for a monster junior season.
Everyone in the back seven is due back, though that’s no longer as much of a given as it used to be with more players who are only projected as mid-round NFL draft picks moving on seemingly every year.