49ers' offensive potential unrealized in 2018 season

The 49ers should have won seven games in 2018, according to head coach Kyle Shanahan.

They won just four, and lost all their road games for the first time since 1979. They fell “far short” of their expectations, according to GM John Lynch. But they have potential, if they figure out why they underperformed and where they must improve.

Here are the 49ers' offensive grades for 2018.

Quarterbacks: B-plus

The 49ers started three quarterbacks because two got hurt. Jimmy Garoppolo tore his ACL Week 3, and C.J. Beathard injured his wrist Week 8. Nick Mullens, the 49ers' third-stringer, statistically was their best quarterback. His passer rating was 90.8. Garoppolo's rating was 90. Beathard's was 81.8. None of them ranked among the NFL's top 20 quarterbacks. Combined, they threw 20 interceptions.

But all three essentially are rookies in terms of game experience. Each has made no more than 10 career starts.

Compared to other novices in 2018, the 49ers trio played quite well. All three posted higher passer ratings than Sam Darnold (77.6), Josh Allen (67.9) and Josh Rosen (66.7) - rookies who were first-round draft picks. The only rookie quarterback who recorded a higher rating than Mullens and Garoppolo was Baker Mayfield (93.7), the No. 1 pick of the 2018 draft.

The 49ers have at least two of the best young quarterbacks in the NFL. If Garoppolo isn't ready to play Week 1 next season, Mullens can run the offense very well. Other teams should be so lucky.

Running backs: A-minus

The 49ers signed starter Jerick McKinnon during the offseason to a four-year, $30 million contract, but he tore his ACL before the regular season even started. His replacement, Matt Breida, played most of the season with an ankle injury and missed two games, but still averaged 5.3 yards per carry - fourth-best in the league among running backs with at least 100 rushing attempts.

Breida's backup, Raheem Mostert, was even more efficient. He averaged 7.7 yards per attempt on just 52 carries before a broken arm ended his season. Both he and Breida played exceptionally well while healthy. Their injuries don't hurt their grades. They got injured because football is violent and running backs take a bigger beating than any other position.

All three should be healthy to start next season. Which means the 49ers will have an electric trio of running backs, plus three-time Pro Bowl fullback Kyle Juszczyk.

Wide receivers: C

The 49ers' top-three receivers from 2017 all struggled while playing through injuries in 2018.

Marquise Goodwin played through a quad contusion, a hamstring injury and a calf strain and got benched after missing five games. The 49ers' quarterback rating when targeting him was 77.2. Kyle Shanahan said he intends to reduce Goodwin's workload next season, which likely means he will remain a backup.

Pierre Garçon played through a knee injury and missed eight games for the second season in a row. The 49ers' quarterback rating when targeting him was 69.7. He will be 33 in August. The 49ers may cut him before the season starts.

Slot receiver Trent Taylor had back surgery during the offseason and never seemed to recover. He averaged only 8.3 yards per catch, and the 49ers' quarterback rating when targeting him was 64.6.

The 49ers' leading receiver was Kendrick Bourne, who gained only 487 yards and started just eight games. He may be a long-term backup rather than a future starter. The 49ers may need to draft or sign a starting receiver this offseason.

Rookie Dante Pettis could be a future starter. He averaged 17.3 yards per catch in 2018, and the 49ers' quarterback rating when targeting him was 113.8. But he injured his knee twice and missed four games. He seems brittle for an NFL wide receiver, because he doesn't yet have an NFL body. He lacks strength and muscle definition. He needs to hit the weight room.

Tight ends: A

George Kittle might be the best tight end in the league. He set the NFL record for receiving yards in a season by a tight end with 1,377, plus he drew eight penalties for an additional 58 yards.

He did all this while opposing defenses game-planned specifically to shut him down.

Kittle may become even more dangerous in the future. In 2018, he caught just two touchdown passes in the red zone out of 22 targets. Expect Shanahan to find new, creative ways to feature Kittle in the red zone next season.

And expect the 49ers to explore adding a new backup tight end during the offseason. The current backup, Garrett Celek, had more penalties (six) than catches (five) in 2018.

Offensive linemen: C

For the most part, the run blocking was good. The 49ers averaged 4.5 yards per carry - 12th best in the league. But the pass protection was among the NFL's worst. The offensive line gave up 48 sacks (ninth most), and 125 quarterback hits (second most).

But the pass protection may improve next season. Right tackle Mike McGlinchey was a rookie in 2018. Center Weston Richburg played through a knee injury he suffered Week 4. And Laken Tomlinson played through a hip injury he suffered Week 13.

Despite the hip injury, Tomlinson played well enough to earn the 49ers' Bobb McKittrick Award for the team's top offensive linemen. Tomlinson tore his MCL during the 49ers' season finale, but could make a full recovery in three months, according to the team.

One offensive linemen who may not improve: six-time Pro Bowl left tackle Joe Staley. He turned 34 in 2018 and showed his age, as he struggled blocking fast edge rushers who use inside counter moves. He will be a free agent in 2020. The 49ers will need to find or develop a new offensive tackle.

That's it for the offense's grades. Defense, special teams and coaches will receive theirs on Thursday.