49ers start mandatory minicamp Tuesday

With more turnover than any other team in the NFL, we preview the 49ers' mandatory minicamp kicking off Tuesday.

SANTA CLARA, Calif. - This week will be the San Francisco 49ers' first chance to see exactly what they have for the upcoming season. That's because they are expecting all their players to participate in the mandatory three-day minicamp starting Tuesday.

Before this week, San Francisco's offseason program was voluntary, which meant key veterans were missing from the practice field. Receiver Anquan Boldin, offensive lineman Alex Boone, kicker Phil Dawson and right tackle Anthony Davis highlighted that list, before Davis retired Friday.

No team in the NFL is facing more turnover than the 49ers, who lost 11 starters from 2014 this spring - four to retirement, six to free agency and one in a trade. Tuesday will be new head coach Jim Tomsula's first chance to make all the new pieces fit on the practice field.

Here's a quick look at some key story lines heading into the three-day session.

Kap's mechanics

Based on what we've seen from the voluntary sessions, Colin Kaepernick's new throwing motion is not drastically different from that of his first three years as starter. This offseason he spent 11 weeks at the football performance facility EXOS in Arizona, working on shortening his release, improving his pocket presence and breaking down film.

The hope is a number of small, nuanced changes lead to a big improvement in Kaepernick's overall game. His stride and release are more compact, which should improve his accuracy, particularly in short-area throws. What remains to be seen is how his pocket presence evolves. Kaepernick's inability to keep his eyes down field while facing pressure in the pocket played a significant role in tacking 52 sacks last year, where San Francisco ranked fourth-worst in the NFL.

The early returns from the voluntary practices indicated new coordinator Geep Chryst is going to make running backs a priority in the passing game, which could help Kaepernick avoid sacks and put the offense in more favorable positions in later downs. Under Greg Roman, running backs were used mostly in pass protection and screens were not a part of the offense. Look for that to change to help to make things easier for Kaepernick in 2015.

Staley's new crew

Both first-round picks from 2010 are gone. Left guard Mike Iupati signed a lucrative free-agent deal with the Arizona Cardinals and Davis left big shoes to fill at right tackle with his recent retirement.

The 49ers have 14 offensive lineman on their offseason roster, and have two open spots to play with as a result of the Andy Lee trade and Davis' retirement. Currently, only two of the five offensive line spots are spoken for. Joe Staley will be the team's left tackle, and Boone will likely play on the right side, either at guard, where he's been the starter since 2012, or at tackle, to replace Davis.

That means offensive line coach Chris Foerster will have his work cut out for him this summer as he tries to piece together the team's new offensive line. "Red-shirt" second-year player Brandon Thomas has been getting the majority of first-team reps at left guard, as expected, but could be in the mix at tackle after playing left tackle at Clemson.

Center Daniel Kilgore has not practiced after sustaining a fracture to his lower leg mid-way through that season, and has not given a timetable for his return. That means second-year player Marcus Martin might be in line to start training camp playing center with the first team. Martin will also compete at both guard spots.

Free-agent acquisition Erik Pears has been getting first-team reps at right guard in Boone's absence, with rookie seventh-round pick Trent Brown playing in Davis' old spot.

Boone, who is entering a contract year, played tackle at Ohio State and would likely push for the right tackle job to give him more appeal on the free-agent market next March. Pears has also played tackle for the majority of his eight-year career. Joe Looney will be in the mix at all three interior positions.

Rotating Corners

There might not be a position group that rotated more during the open voluntary sessions than the cornerbacks. The 49ers lost both starters, Chris Culliver and Perrish Cox, to free agency, and expect Tramaine Brock to assume a starting job after earning his four-year contract extension in 2013, when he became the team's best corner after starting the season as a reserve. But Brock has practiced sparingly this spring after a bad toe injury sidelined him for 13 weeks last season.

Including nickel corner Jimmie Ward - who has not practiced this offseason while recovering from his second Jones fracture in his foot in as many seasons - San Francisco has 10 corners on the offseason roster. The competition for jobs is more wide open than anywhere else on the team.

Free-agent pickup Shareece Wright and Dontae Johnson appear to be the favorites for the second and third spots on the depth chart. But Keith Reaser, Kenneth Acker, Chris Cook, Marcus Cromartie, Mylan Hicks and Leon McFadden are muddled in a very close competition that will sort itself out before the start of the regular season.

Bowman's Health

NaVorro Bowman has been on the practice field sparingly this spring while recovering from his torn ACL and MCL in his left knee sustained in January 2013. The media has been privy to just one of the practices he participated in, and it was clear he was still a long way from returning to his All-Pro form.

Last month, Bowman said his knee is still "inconsistent". At this point in the offseason, expect Bowman to take it easy and continue getting a small number of reps. He's juggling learning a new defense while getting his knee ready for training camp, and the coaching staff will keep him on a limited rep count this week.

Follow Chris Biderman on Twitter.

Next story:

49ers, inevitably, trade punter Lee to Browns

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