Grant Cohn: Five biggest questions 49ers will face in training camp

The 49ers are on their final vacation of the offseason. When they return for training camp at the end of July, here are the top-five questions they must face.

1. Will Anthony Davis ever come back?

The 49ers seem to expect he'll come back soon. They didn't sign or draft a replacement this offseason, nor did they give away Davis' jersey number to a new player. Whenever Davis decides he wants to play again, he can have his old job, his old No. 76 and probably his old locker and parking spot, too. Whatever he wants. Just come back, please. That's the message the Niners are sending.

Davis is sending mixed messages in return. On July 12 the retired offensive lineman tweeted, 'I will play ball.' Then he deleted the tweet. Why? He also hasn't filed for reinstatement with the National Football League. Why? What is he waiting for? Is he not healthy? Is he not in shape? Is he overweight? Is he underweight? Is he fit to play this year, or does he need another year off? Will he even show up for training camp, or will he show up Week 1 and expect to play? Or will he never play again?

If he plays next season and still is in shape, the Niners could have a good offensive line. The Niners are at Davis' mercy.

2. Will DeForest Buckner make a significant impact?

The Niners chose to put themselves at Davis' mercy.

With the seventh pick in the draft, the Niners took DeForest Buckner, a defensive lineman, instead of Jack Conklin, an offensive lineman who could have filled the biggest hole on the Niners roster — right tackle. The Titans drafted Conklin one pick after the Niners took Buckner.

Conklin already is a starter — he played with the Titans' first-team offense during minicamp. 'He's exactly what we were hoping for to fill that spot,' Titans head coach Mike Mularkey said recently.

Meanwhile during 49ers minicamp, Buckner played not with the first-team defense, not with the second-team defense, but with the third-team defense. With the undrafted rookies and the players who won't make the team.

Buckner of course will make the team and probably will have a terrific career. He has talent. But how much impact will he make as a rookie? Will he start? Can he stop the run, or will he play only on third downs? Will he be a pass-rushing specialist? And how good of a pass-rushing specialist can he be? How many sacks will he get? How will he affect the 49ers' win-loss record next season? Will he affect it at all?

3. Will the 49ers stop the run under new defensive coordinator Jim O'Neil?

Jim Tomsula couldn't coach an entire football team, but he could coach run defense. During the nine years he spent with the 49ers — eight as the defensive line coach and one as the head coach — the defense never ranked worse than 12th against and run and never gave up more than 4 yards per carry in a season.

New defensive coordinator Jim O'Neil does not have a good track record coaching run defense. He's a former defensive backs coach who specializes in coaching pass defense. His first season as an NFL defensive coordinator — 2014 with the Browns — his defense ranked 28th against the run. In 2015, his defense ranked 27th against the run. It ranked eighth in that statistic the season before he got hired.

Will O'Neil have the same negative effect on the 49ers run defense? Can the team stop the run without Tomsula?

4. Can Chip Kelly manufacture a quality offense with the current players?

In 1978, the 49ers offense ranked 27th in a 28-team league. Then the team hired Bill Walsh and during his first season as head coach the offense ranked sixth. Walsh showed brilliance right away even though he won just two games that season.

Will Kelly show brilliance right away?

No one expects him to win much. The Niners currently are underdogs in every game next season Weeks 1 through 16. But can Kelly at least create a successful offense to build his team around like Walsh did?

Kelly takes over an offense that ranked 31st out of 32 teams last season. An offense that has probably the worst group of wide receivers in the NFL, two new starting guards and no set starter at right tackle or quarterback.

But it also has Carlos Hyde, one of the most talented young running backs in the league when healthy. Hyde fits Kelly's offense perfectly, because Hyde prefers running from shotgun formations — that's what he did at Ohio State. He absolutely has to have a huge season for Kelly's offense to succeed. Can Kelly count on him?

5. Will Kelly's system bring out the best in Colin Kaepernick?

Or will it bring out the best in Blaine Gabbert? Gabbert is a mobile quarterback, plus he doesn't hold the football too long in the pocket. He speed reads the defense and quickly releases the ball, just as Kelly wants his quarterbacks to do.

Kaepernick is a much less decisive passer. Sometimes he looks utterly confused in the pocket. And he takes forever to throw. Will this change under Kelly?

Kaepernick's best chance to beat out Gabbert probably will come during preseason when Kaepernick can showcase his greatest ability — his speed. If he runs for a few big gains and makes the ground attack more effective than Gabbert does, Kaepernick could start Week 1 against the Rams.

Run, Colin, run.

Grant Cohn writes sports columns and the 'Inside the 49ers' blog for The Press Democrat's website. You can reach him at grantcohn@gmail.com.