Five keys for the 49ers this season

The 49ers are the biggest mystery in the NFL.

They were bad for nine weeks last season. They dropped passes, missed assignments on defense and generally played like the worst team in the league. They couldn’t win. They began the season 0-9.

Then, they traded for Jimmy Garoppolo, and won five games in a row. For a little more than a month, the 49ers couldn’t lose. They even beat the Jacksonville Jaguars by 11 points, and that team went on to the AFC Championship Game. Garoppolo changed everything for the 49ers. He was magical.

Now, the 49ers don’t know which team they are, although they hope they’re the team from the final five games of last season. They don’t know if they’re good, bad or mediocre. They could go to the Super Bowl or finish last in the NFC West. Both predictions are entirely possible and plausible. So much is unknown about them.

Here’s what is known:

Garoppolo will give them a chance to win every week

He’s that good. He has the ideal skillset for a quarterback - strong arm, quick release, accuracy, willingness to throw into tight windows, mobility and poise. He plays with the confidence of a 15-year veteran. He’s Joe Cool 2.0.

Last season, his quarterback rating with the 49ers was 96.2. Impressive, considering he hardly knew the playbook, and didn’t have wide receiver Pierre Garcon, who was out with a fractured neck. They never played together. The 49ers’ No. 2 receiver was rookie Kendrick Bourne.

Now, Garcon is back, and Garoppolo knows the entire playbook. The 49ers should remain competitive as long as they keep Garoppolo upright and healthy.

The right side of the offensive line may be a problem

The 49ers have three new starters on the offensive line – center Weston Richburg, right guard Mike Person and right tackle Mike McGlinchey. They didn’t participate in the 49ers’ five-game win streak to end last season, because they weren’t on the team. The Niners acquired them this offseason.

Richburg came from the New York Giants, where he missed 12 games last season with a concussion. Person came from the Indianapolis Colts, where he started four games at center. He never has started at guard. And McGlinchey came from Notre Dame. He’s a rookie.

Defenses will take turns isolating and testing each player. They’ll put their best edge rusher across from McGlinchey instead of the veteran on the left side, Joe Staley. They’ll put their best interior rusher across from Person. And they’ll put a nose tackle across from Richburg to see if he can block someone by himself without help from a guard.

If the right side of the offensive line plays well, Garoppolo should have a good season. If the right side of the offensive line doesn’t play well, the consequences for Garoppolo could be catastrophic.

Jerick McKinnon’s knee injury may hurt the offense

From the day the 49ers signed McKinnon to the day he tore his ACL - almost six months - they designed their offense around him. Not only the run game, but the pass game, too.

McKinnon was supposed to give the offense an element it lacked last season: A running back/wide receiver hybrid who could make the offense unpredictable and explosive.

But, McKinnon went down just eight days before the season opener. Now, 49ers head coach Kyle Shanahan must adjust on the fly, and erase the sections of the playbook that feature McKinnon.

The 49ers have no other running backs like him.

The new starter, Alfred Morris, is not a running back/wide receiver hybrid. He’s just a running back - he has caught only 57 passes since entering the league in 2012. He’s similar to Carlos Hyde, the previous starter.

The 49ers wanted to evolve on offense this season. Now they have to re-create the past, or find a different way to evolve. Along with Darwin, Shanahan is an expert when it comes to theories of evolution.

The pass rush needs ?to prove itself

The 49ers ranked tied for 26th in sacks last season. Then, they brought back the same pass rushers for this season, minus the team’s sack leader, Elvis Dumervil. He retired.

But, the 49ers still think the pass rush will improve.

DeForest Buckner is one of the best defensive tackles in the NFL. He recorded only three sacks last season, because offenses blocked him with two guys. Offenses always will double-team Buckner until someone on the 49ers shows he can beat a single block some of the time, freeing up Buckner from continual double teams.

Defensive coordinator Robert Saleh wants to create one-on-one matchups for Buckner this season. So, at times on third down, Saleh will move Buckner to defensive end, where he can rush one-on-one against an offensive tackle. Meanwhile, the interior rushers will be Solomon Thomas and Arik Armstead, two former first-round picks.

The 49ers didn’t use this configuration last season. It is experimental and may be highly effective.

The pass coverage ?needs to prove itself

The 49ers defense gave up 27 touchdown passes and recorded only 10 interceptions last season. It ranked 22nd out of 32 teams in yards allowed through the air.

To improve the pass defense, the 49ers signed Richard Sherman. He is an all-time great cornerback, but he’s 30 and coming off two offseason Achilles’ tendon surgeries.

During training camp, he would pull himself out of drills after just a few plays. He can’t do that during games. The 49ers have to find ways to rest the best player in their secondary to keep him effective.

The rest of the defensive backs are young and unproven.

They need help. They need a pass rush. Even if Sherman returns to form, the 49ers can’t cover all day. A lethal pass rush means everything to the 49ers defensive backs, to the entire defense.

Let’s see what the 49ers have.