This is the fourth in an eight-part series reviewing the 2016 Vikings and looking ahead by position. Previously: OL / RB, TE / WR

A turbulent season for the Vikings offense began with Teddy Bridgewater's severe knee injury and ended with Sam Bradford being named their starter moving forward. As you know, Vikings General Manager Rick Spielman dealt a 2017 first-round pick and 2018 fourth-round pick to Philadelphia to acquire Bradford just days before the regular season opener.

Because of Bradford, quarterback play was not the 28th-ranked offense's biggest worry as they cycled through offensive tackles and running backs to no avail at either position. Moving forward, Bradford and expected full-time offensive coordinator Pat Shurmur will form the offense's front as Bridgewater recovers.

Quarterbacks

Under contract in 2017: Sam Bradford, Teddy Bridgewater, Taylor Heinicke

Pending free agents: Shaun Hill

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Grades are based on a 1-5 scale, with '5′ marking an excellent season, '4′ for above-average, '3′ for average, '2′ for below-average and '1′ for failure to perform. Players who did not accrue a season (weren't on the active roster for at least six weeks) or played in three games or fewer are not graded. Based on game and practice observations, weekly film reviews and interviews.

Sam Bradford (4.0): Traded from the Eagles to the Vikings eight days before the regular season opener. Started 15 days after the trade and completed 22 of 31 throws for 286 yards and two touchdowns in the U.S. Bank Stadium-opening win against Green Bay. He was then forced to navigate an offense that never generated a ground game, changed coordinators and would lose three offensive tackles to season-ending injuries. Showed some pain tolerance. Sacked a career-high 37 times while leading a passing attack that ranked 18th in yards/game and 21st in touchdowns. To keep him upright, Bradford's throws were shortened even more when Pat Shurmur and a horizontal pass game stepped in for the resigned Norv Turner as play caller. Earned the NFL record for completion percentage (71.6) while averaging the shortest average throw by depth (6.6 yards) in the league, according to Pro Football Focus. Only Kansas City's Alex Smith (6.9) also had an average depth of fewer than seven yards. All things considered, Bradford's individual season was a success while throwing for 3,877 yards, 20 touchdowns and five interceptions against defenses that knew he had no running game and subpar protection. Played 978 snaps [93%], hitting a $1 million escalator for next season's salary for surpassing 90 percent of snaps. One of the league's more accurate downfield passers, ranking eighth in 'deep' target precision, per Pro Football Reference. Flagged eight times. Fumbled 10 times, losing five. Lost the Thanksgiving game to the Lions with an interception on a poor decision into trap coverage. Led the potential game-winning drive in the first loss to the Lions, prior to the botched kickoff and defensive collapse. Also threw a critical fourth-quarter pick in the loss at Washington against a zone blitz. Named the starter moving forward by head coach Mike Zimmer, which seemed inevitable given the uncertain timetable for Bridgewater's recovery. Turned 29 in November. Under contract for an $18 million salary cap hit next season, currently ranking in the middle of the league among starters. It's the final year of his deal, which could spark action this spring should either side seek a long-term commitment.

Shaun Hill (N/A): Made his first start in two years during the season-opening win against the Titans. Completed 18 of 33 passes for 236 yards and no touchdowns or interceptions in Tennessee. Returned to the backup role following the trade for Bradford. Spelled Bradford for two plays against the Cowboys after the starter took a big hit. Played 74 snaps [7%] overall. Turned 37 on Monday. Pending free agent.

Teddy Bridgewater (N/A): Entered his third NFL season with high hopes before a freak non-contact injury now threatens his football future for 2017 and beyond. Dislocated his knee and tore multiple ligaments, including his ACL, according to the Vikings, while dropping back to pass during a routine practice drill Aug. 30. The team said he did not suffer any arterial or nerve damage. Handed the public relations staff a handwritten statement, which ended by saying: "My purpose will not be denied." Had a strong preseason with 18 of 23 passes completed for 253 yards and two touchdowns in two starts. Held out of the second preseason game due to a right shoulder injury. This season also saw the departure of Norv and Scott Turner, the coordinator and quarterbacks coach who led the search that landed Bridgewater in the 2014 draft. Has a fifth-year option that could be picked up this spring, otherwise he'll enter the final season of his rookie contract in 2017.

Taylor Heinicke (N/A): The second-year Old Dominion product missed the preseason and start of the regular season on the non-football injury list after severing two tendons in his ankle during a July accident. Heinicke said he was helping a friend locked out of his apartment when he kicked in a glass pane of a door. Returned to practice in October and was inactive for the final eight games.