This upcoming 2014 NFL season, a wide variety of relatively unheralded sophomore and third year players will inherit or take over key roles for even the best teams in the NFL. Whether it's an already-established starter that will now be assuming more responsibility, or a green, untested player that will now look to become a reliable backup, every roster depth chart has a few big question marks.

I'll break it down team by team, looking at "who" the player is, "where" he plays, "why" he'll potentially play a key role in 2014, and "how" he'll succeed in that.

Today, let's take a look at the San Francisco 49ers.

San Francisco 49ers

S Eric Reid

Who: San Francisco's first-round pick in 2013. Started all 16 games as a rookie. Made the Pro Bowl. Pretty good start.

Where: Free safety. So, all over the field.

Bob Martin-USA TODAY Sports

Why: I include Reid here despite the fact he's already an established starter and first-year Pro Bowler, because the Niners have lost the other three starters that played beside him in 2013 to free agency. With Donte Whitner, Tarell Brown, and Carlos Rogers now gone, Reid likely becomes the on-field leader and "the man" in the defensive secondary for San Francisco. That's no small thing, but his rookie year showed he's up to the task.

How: Take on a more active leadership role. Keep building on a solid first season.

WR Quinton Patton

Who: Patton was a fourth-round pick by the Niners in 2013 out of Louisiana Tech. He's a highly athletic (4.48 40, 37" vert) receiver that was fairly highly touted but coming out of a small school. He only caught three passes in his rookie year, but there are high hopes for 2014 in San Francisco.

Where: The Niners will have a healthy Michael Crabtree to pair with Anquan Boldin this year, but with rumors that the Niners will throw more and move to '11' personnel more often this year (3WR sets), that third receiver spot becomes important. This is the role that Patton will be threatening for.

Why: Patton will face heavy competition from Stevie Johnson and Brandon Lloyd (and Bruce Ellington), but if he can demonstrate consistency in catching the football along with precision in his routes, (plus chemistry with Colin Kaepernick), the team may prefer to go with the homegrown talent in the slot.

Mark J. Rebilas-USA TODAY Sports

How: Patton couldn't find his way onto the field much as a rookie - a common theme with first-year receivers - but has the chance to make a big jump in 2014. He's no sure thing, of course, but in terms of guys that have an opportunity to carve out a bigger role for themselves, Patton could be up there. He'll have to learn to do the little things necessary of an NFL receiver -- timing, intensity, physicality, precision, knowledge of the playbook and any option routes or sight adjustments therein.

It's a big jump from Louisiana Tech to the NFC West, but he ended his first season on a high note, making this nice grab Week 17 against the Cardinals, a catch that put the Niners into field goal range with under a minute left. They hit the field goal, and won.

TE Vance McDonald

Who: McDonald was a second-round pick by the Niners in 2013. He caught 8 passes for 119 yards his rookie year in backup/tandem duties to/with Vernon Davis. He's another physical freak of nature at 6'4, 267 pounds with long arms and big hands, and the potential is certainly there. However, his rookie season was probably a bit of a disappointment.

Where: McDonald has the chance to continue to carve out a role as the second tight end in two tight end sets and as Vernon Davis' primary backup. He has the capability to be used as a de facto fullback in some of the Niners' diamond formations and heavy sets. McDonald played 480 snaps in his rookie year (48.4 percent of SF's total), and his role will likely only expand as he gets more comfortable.

Kelley L Cox-USA TODAY Sports

Why: The Niners may in fact throw more and move to more one tight end sets in 2014, but they're still a run team, and that's where McDonald can shine. He will never be the pass catching threat that Vernon Davis is -- he's plenty athletic, for sure -- but his value is as a dual-threat tight end that's as strong blocking as he is running routes. Additionally, with the Niners' heavy use of tight ends in their offense, he's a valuable backup to Davis.

How: Display better concentration seeing the ball into his hands. Make an impact in the run game. Play physically. Keep learning the offense. McDonald came to San Francisco via Rice, which, like Patton, is a pretty big jump.

OLB Corey Lemonier

Who: San Francisco chose Lemonier in the third round of the 2013 NFL Draft, out of Auburn. Lemonier was a part of Auburn's 2011 National Championship team, and was an All-SEC pick the next year with 9.5 sacks. He followed up his junior year with 5.5 sacks.

Where: Lemonier plays outside linebacker for the Niners, lining up on both the right and left side. In that role, he's mainly asked to rush the passer, but he also dropped into coverage at times, and showed an ability to play the run as well.

Kirby Lee-USA TODAY Sports

Why: Aldon Smith's immediate future with the Niners is still up in the air after pleading no contest to felony weapons charges. It's unclear if the NFL will suspend Smith (or whether he'll actually face incarceration), but it's a safe bet that he'll miss time in 2014. That means the Niners will again turn to Lemonier, along with Dan Skuta, to fill the enormous void Smith's absence creates. Lemonier filled in for an absent Smith during his rookie year as well, and performed reasonably well in that difficult role - and will look to build on that experience in year two.

How: Lemonier doesn't have a dizzying amount of pass rush moves, utilizing speed off the edge or a bullrush most commonly. He does, however, have a nice punch/jab and uses a solid hand to the chest of an opposing tackle to convert speed to power. He's got nice size, nice speed, can drop fairly effectively, and he certainly looks the part. He could have a pretty big role for the Niners in 2014.

Some examples of Lemonier collapsing the pocket from the right side, against the Texans last year. He also rushes (more commonly) from the left side (where Smith normally lines up).

C Daniel Kilgore

Who: Kilgore might be the longest-tenured player in this entire series, entering his fourth season after being selected by the Niners in the fifth round in 2011. He has played an important backup role his first three years and has experience in 33 games.

Where: However, he's currently slated first on the depth chart at center for the Niners, who have one of the best offensive lines in the game and rely on a relatively complicated pulling and trapping run game. That's no small thing for a guy with zero NFL starts.

Matt Kartozian-USA TODAY Sports

Why: The Niners declined to re-sign veteran center Jonathan Goodwin, who started the last 48 games for the Niners.

How: Kilgore will have to beat out rookie Marcus Martin for the job, but considering he has a few years of seasoning in the playbook and at the NFL level, he's probably the favorite, at least to start out. He'll have to prove he can function in Greg Roman's offense, which requires a high level of athleticism to go along with fierce toughness and physicality.

DT Tank Carradine

Who: San Francisco selected Carradine in the second round of the 2013 Draft out of Florida State University. He was hailed then as an extremely strong, absurdly athletic physical specimen at the defensive end spot that registered 11 sacks and 13 tackles for a loss his senior year, but only fell to the second round because of a torn ACL. He was a "redshirt" player for the Niners his rookie year.

Where: Tank figures to be a long-term heir apparent to Justin Smith, so he'll likely see most of his snaps at the defensive end spot, but could also figure in as a nickel defensive tackle. He's not experienced in a 3-4 defense but projects well in one.

Mitch Stringer-USA TODAY Sports

Why: Justin Smith's play hasn't yet trailed off, but at 34 years old, the Niners may want to start developing his replacement. Carradine is a work in progress, surely, but has the natural talent to potentially fill Smith's shoes. It won't likely be this season barring injury, but getting him into the rotation should help San Francisco keep everyone on their defensive line fresher longer, and it gives them more looks schematically. Putting Carradine next to Aldon and/or Justin Smith will give opposing offensive coordinators headaches.

How: Tank put about 20 pounds of muscle on during his rookie red-shirt season, and is now up to 295 pounds. If he has retained his quickness and power that were so apparent at Florida State, he'll find himself a role quickly, likely on passing downs early on. He does have the potential to be an every-down player eventually.

RB Marcus Lattimore:

Who: A fourth round pick by San Francisco in the 2013 NFL Draft, Lattimore sat out his rookie season rehabbing a torn ACL (much like Tank Carradine). Lattimore was a superstar at South Carolina prior to his devastating injury.

Where: Backup running back, because Frank Gore never ages, apparently.

Jeff Blake-USA TODAY Sports

Why: Well, Gore isn't getting any younger, in theory. The Niners love to run the football with power, and that means, generally speaking, that their backs will take a lot of punishment. San Francisco has a very deep running back group, but Lattimore is certainly the wild card -- possessing elite talent but a big question mark with his health. Kendall Hunter, Carlos Hyde, and LaMichael James will also compete for the job

How: Do this stuff. Also, stay healthy.