The NFL salary structure isn't a perfect system where performance matches compensation. This is particularly true of draft choices because their salaries are dictated by draft position.

Timing matters with veteran contracts. The running-back market is experiencing an unprecedented economic downturn, while the consistent growth in the salary cap has led to salaries escalating at most positions. Highly productive older veterans, except quarterbacks, can have difficulty getting lucrative long-term deals because teams are afraid of a drop off in play as these players age.

Here's a look at some of the NFL's most underpaid players on veteran contracts. Players on rookie contracts were excluded. Overall contract packages were evaluated, in addition to 2017 compensation.

Offense

Contract Value: $60 million/4 years ($15 million per year average)
2017 Compensation: $1 million
Future Compensation: $15 million-2018; $15 million-2019

Brady started taking a unique approach to his contracts in 2013 when he first renegotiated the 2010 contract extension which made him the NFL's highest-paid player. He began consistently giving the Patriots hometown discounts instead of driving the market.

Brady's third renegotiation since signing the 2010 deal, in March 2016, added two years for $41 million running through the 2019 season, when he will be 42 years old. This 2016 renegotiation covers four years for a total of $60 million. The new money Brady will receive through his multiple contract maneuvers compared to what he would have gotten had he played out his 2010 contract, which was set to expire after the 2014 season, is $71 million over five new contract years for an average of $14.2 million per year.

Brady is having the finest season in NFL history for a quarterback after turning 40. He is a leading candidate to win NFL MVP for the third time in his 18-year career. Brady is averaging the second-most passing yards per game (306.7), has the second-best completion percentage (68.4) and third-best passer rating (111.7) of his career. His passing yardage and passing rating are tops in the NFL. Brady's completion percentage is third best in the league. He is also second in the NFL with 26 touchdown passes.

Brady's approach to his contracts has paid dividends in allowing the Patriots to assemble a more talented roster than they would have otherwise, which has resulted in two more Super Bowl rings since starting the process. Other upper echelon quarterbacks haven't followed Brady's lead by signing discounted contracts.

Contract Value: $2 million/1 year (worth up to $2.25 million with incentives)
2017 Compensation: $2 million
Future Compensation: In Contract Year

The Vikings signed Keenum strictly for depth almost a month into free agency. He has been the ultimate insurance policy with 2016 starting quarterback Sam Bradford's ailing left knee limiting him to six quarters of action this season and 2014 first-round pick Teddy Bridgewater, Minnesota's 2015 starting quarterback, recently returning from last preseason's devastating knee injury that put his career in jeopardy.

The Vikings are in firm control of the NFC North and in contention for a first-round playoff bye. Eight of Minnesota's nine victories have come with Keenum under center. He is making it very difficult for head coach Mike Zimmer to switch quarterbacks despite Bridgewater's availability. Continuing to erase perceptions that he is nothing more than a quality backup or stop-gap starter could put Keenum in line for the type of money Mike Glennon, with less of a track record, received from the Bears in the offseason ($45 million over three years).

Contract Value: $16 million/4 years ($4 million per year average)-$16.6 million maximum with salary escalators
2017 Compensation: $3.7 million
Future Compensation: $4.6 million-2018 (voids with AP 1st team All-NFL selection in 2017)

There was speculation that Ingram's production would decline with the offseason additions of Adrian Peterson in free agency and Alvin Kamara through the NFL draft. Quickly deemed as expendable, Peterson was traded to the Cardinals early in the regular season.

Ingram had his first 1,000 rushing yard season in 2016. He's having a career year while forming the NFL's most dangerous running back tandem with Kamara. He's fifth in the NFL with 837 rushing yards. His 1,055 yards from scrimmage (combined rushing and receiving yards) are sixth in the league. Ingram's production over the last two seasons has been comparable to the Falcons' Devonta Freeman, who signed the most lucrative long-term running back deal, averaging $8.25 million per year in the preseason. A nice raise could be awaiting Ingram if he is a free agent. His 2018 contract year, worth $4.6 million, voids if he is selected first team All-NFL this season by the Associated Press.

Contract Value: $1.25 million/1 year
2017 Compensation: $1.25 million (worth up to $2.8 million with incentives)
Future Compensation: In Contract Year

Blount languished on the open market for a second straight year despite a career-high 1,161 rushing yards (eighth in the NFL) and a league-leading 18 rushing touchdowns in 2016. He didn't find a home until several days after the NFL draft in early May. Blount is spearheading the NFL's second-most potent rushing attack with 658 yards, which ranks 10th in the NFL.

Contract Value: $19.246 million/4 years ($4,811,500 per year average)-$28.546 million through salary escalators and incentives
2017 Compensation: $6.746 million (includes $4 million signing bonus)
Future Compensation: $3.5 million-2018; $4 million-2019; $5.5 million-2020

Thielen has taken his game to a different level this season after a breakout 2016 campaign in which he caught 68 passes for 967 yards with 5 touchdowns. He's already become the first Vikings player to reach 1,000 receiving yards in a season since Sidney Rice in 2009. Thielen's 1,005 receiving yards are the third most in the NFL. He's in a tie for fourth with 70 receptions. Thielen has been the hallmark of consistency in 2017. He is the only player to catch at least five passes in every game this season.

Thielen is giving the Vikings the type of production expected out of Greg Jennings when he signed a five-year, $45 million contract (worth a maximum of $47.5 million through salary escalators and incentives) in 2013, while the salary cap was $123 million. The Jennings contract is the equivalent of a deal averaging a little more than $13.5 million per year under the current $167 million salary cap.

Thielen was scheduled to make $2.7 million as a restricted free agent before signing a four-year deal in April, in which he gave up three unrestricted free-agency years for $16.5 million. These years can be worth as much as $25.8 million with outstanding performance during the contract. Thielen's 2018 base salary has already increased from $2.85 million to $3.35 million because he has caught 70 passes. It goes up another $250,000 with 80 receptions and tops out at $3.85 million if Thielen reaches 90 catches.

Contract Value: $13.375 million/2 year extension ($6,687,500 per year average)-$14.45 million maximum with incentives
2017 Compensation: $4.5 million
Future Compensation: $6.2 million-2018

Walker has been Marcus Mariota's security blanket ever since the quarterback was selected second overall in the 2015 draft. His production is comparable to the game's best young tight ends, Zach Ertz and Travis Kelce. Walker's 212 receptions since the start of the 2015 season are second most in the NFL for tight ends. He is sandwiched between Kelce's 219 catches and Ertz's 208. Walker's 2,501 receiving yards during this span trails only Kelce, who has 2,777 yards, among tight ends. Ertz and Kelce are on long-term extensions averaging in the $9 million per year neighborhood.

Contract Value: $9 million/3 year extension ($3 million average per year)-worth up to $11.1 million with incentives
2017 Compensation: $2.515 million (includes $1.6 million signing bonus)
Future Compensation: $1.3 million-2018; $2.4 million-2019; $3.4 million-2020

The Patriots were smart to lock up the 2015 undrafted free agent shortly after he became eligible for a contract extension. Andrews has emerged as one of the NFL's better centers this season. Since Andrews wasn't drafted, the Patriots were probably going to give him a second-round restricted free agent tender in 2018, which will be approaching $3 million, if he had played out his rookie contract. He essentially gave up two unrestricted free agent years for a total base value of $6 million. This season, Andrews has been outperforming Jaguars center Brandon Linder and Seahawks center Justin Britt, both 2014 draft picks who signed extensions averaging $10.34 million and $9 million per year during the preseason.

Contract Value: $2.746 million/1 year
2017 Compensation: $2.746 million
Future Compensation: In Contract Year

The Panthers made Trai Turner, Norwell's counterpart at guard, a signing priority in the offseason. Norwell has been at least his equal on the field over the last two seasons. Turner received a four-year, $45 million extension with $20.5 million in guarantees.

Norwell could be the next big beneficiary of the explosion in offensive guard salaries. It will likely take a contract similar to Turner's for Carolina to keep one of the NFL's best guard tandems from breaking up after the season. Carolina designating Norwell as a franchise player is unrealistic. He would receive a one-year financial windfall because the franchise tag doesn't account for the salary differences at the three main offensive line positions (center, guard and tackle). The 2018 offensive line number should be around $14.5 million. An unrestricted free agent has set the guard market in each of the last two years. Norwell eclipsing the five-year, $60 million deal containing $31.5 million in guarantees Kevin Zeitler received from the Browns is possible if he tests the open market.

Defense

Contract Value: $26 million/4 years ($6.5 million per year average)
2017 Compensation: $6.5 million
Future Compensation: $6.75 million-2018

Graham has been thriving in the attacking 4-3 scheme Jim Schwartz installed once he was named defensive coordinator in 2016. His 83 quarterback pressures last season were the third most in the NFL, according to Pro Football Focus. One of the two players Graham trailed was Giants defensive end Olivier Vernon, who signed a five-year, $85 million contract containing $52.5 million of guarantees in 2016. Graham already has a career-high seven sacks this season.

The Eagles are reportedly working on a well-deserved extension with Graham, according to CBS Sports NFL Insider Jason La Canfora. He's playing on a contract that was adjusted in the preseason, when $1.5 million of performance bonuses were added. Graham earned a $250,000 incentive and a raised his 2018 base salary from $6.5 million to $6.75 million when he got his seventh sack. Reaching nine sacks, making the Pro Bowl, or being named first- or second-team All-NFL will bring his incentive total to $500,000. Graham's 2018 base salary can escalate another $250,000 with nine sacks. Twelve sacks would increase it an additional $250,000. A Pro Bowl selection or All-NFL honors would also add $250,000 to his 2018 base salary.

Contract Value: $53.327 million/5 year extension ($10,665,400 per year average)
2017 Compensation: $7.6 million
Future Compensation: $9.55 million-2018

Besides Rams defensive tackle Aaron Donald, nobody is more disruptive to the opposition's passing game from the interior of the defensive line than Atkins. In fact, Atkins has the most sacks among interior defensive lineman since the start of the 2015 season with 26.5. The market for defensive tackles dramatically changed after Atkins signed his extension in 2013. The top run stuffers are signing deals in the $12 million per year range while the best pass rushers are getting upwards to $17 million per year. Donald is expected to become the NFL's first $20 million per year non-quarterback when he signs an extension, which most likely will occur sometime in 2018.

Zach Brown
ILB

Contract Value: $2.3 million/1 year (worth up to $4.65 million through incentives)
2017 Compensation: $2.3 million
Future Compensation: In Contract Year

Brown couldn't capitalize on a breakout 2016 season with the Bills, in which he played in the Pro Bowl and was second in the NFL with 149 tackles. He bet on himself with a "prove it" deal after failing to find a satisfactory long-term deal in free agency. The speedy tackling machine has picked up where he left off last season despite a change of scenery. Brown leads the NFL with 110 tackles. He should be mindful of the recent payment history with non-pass rushing linebackers. The big deals have come staying put rather than going elsewhere on the open market. Christian Kirksey (Browns), Alec Ogletree (Rams), Vontaze Burfict (Bengals) and Telvin Smith (Jaguars) have gotten contract extensions from their respective teams averaging between $9.5 million and $11.1 million per year during the last few months.

Contract Value: $15.3 million/3 years ($5.1 million per year average)
2017 Compensation: $4.25 million
Future Compensation: $4.25 million-2018

Hayward was arguably the best defensive player signing in free agency last year. He earned his first Pro Bowl berth in 2016 after leading the NFL with seven interceptions. Hayward has solidified his place among the NFL's top cornerbacks by continuing to perform at a Pro Bowl level this season. His 11 interceptions since the start of the 2016 season are an NFL best. This year's top cornerback deals have been in the $14 million per year neighborhood with overall guarantees ranging from $26 million to $41 million.

Contract Value: $775,000/1 year
2017 Compensation: $775,000
Future Compensation: In Contract Year

Robinson landed with the Eagles on a minimum salary deal after the Colts released him following an injury-plagued 2016 season. Originally slated to cover slot wide receivers as a nickel cornerback, Robinson has received more extensive playing time because of Ronald Darby's dislocated right ankle in the season opener that sidelined him for eight games. Robinson has been up to task with his blanket coverage. He's tied for the team lead with three interceptions.

Contract Value: $2.25 million/1 year (worth up to $4.65 million with incentives)
2017 Compensation: $2.25 million
Future Compensation: In Contract Year

Branch was in danger of being a salary cap casualty before nearly cutting his 2017 salary in half to remain in Arizona. He was scheduled to make $4 million in the second year of a two-year, $8 million contract (worth a maximum of $10 million with incentives) before the renegotiation. The inclusion of incentives gave Branch the opportunity to make back the lost money.

Branch may have been having the best season of Arizona's star-studded secondary, which includes six-time Pro Bowl cornerback Patrick Peterson and safety Tyrann Mathieu, before tearing the ACL in his right knee during a Week 10 loss to the Seahawks. He is still leading the Cardinals with 69 tackles. Branch was also Pro Football Focus' fourth highest graded safety this season when injured.

The injury is costly one for Branch. He was on track to earn $1.75 million in playtime incentives because he was playing over 90 percent of Arizona's defensive snaps. He is going to make only $250,000 instead, because his season playtime will be above 40 percent. Branch also has $900,000 in game day active-roster bonuses ($56,250 per game), which are considered as a part of his $2.25 million salary. Since he is out $393,750 for missing the final seven games, his total compensation for this season will be a bit over $2.1 million including the incentives earned.

Special Teams

Contract Value: $6.75 million/3 years ($2.25 million per year average)-$9.75 million maximum with incentives
2017 Compensation: $2.125 million (includes $750,000 signing bonus)
Future Compensation: $2.3 million-2018; $2.325 million-2019

Zuerlein has rebounded nicely from a horrific 2015 season in which he made only 66.7 percent of his field goal attempts. Since then, he has been the NFL's fifth most accurate kicker, converting 91.1 percent of field goals.

Zuerlein is having a historic 2017 season. He is on pace for 188 points, which would shatter the NFL kicker scoring record of 166 points set by David Akers in 2011 with the 49ers. Zuerlein is also on track to break former Chargers running back LaDainian Tomlinson's record of 186 points for any position, set in 2006. He has made 32 of 34 field goal attempts (94.1 percent) and hasn't missed an extra point this season.