NEW YORK — Established superstars such as Tom Brady or Aaron Rodgers grab all the attention when their teams do well.
But a team's success or failure can often be determined by which players make the biggest jump from year to year.
Key players such as Kansas City's Patrick Mahomes and Pittsburgh's James Conner have played major roles in their respective teams being in first place through Week 9.
And it isn't always offensive players. Of the 32 teams, nearly half (15) have featured a defensive player and one had a kicker among the most improved.
At the halfway point of this NFL season, here's a look at the most improved players for each team:
New England: Linebacker Kyle Van Noy. The Patriots traded for Van Noy out of necessity two years ago. He's grown into one of the most versatile players on New England's defense. Used almost exclusively at outside linebacker last season, he's now asked to play on the line at times, is an option in multiple blitz packages as well as in zone and man coverages.
Miami: Offensive tackle Laremy Tunsil. Tunsil is becoming a top-shelf left tackle in his third season. He was plagued by penalties and other lapses, but has benefited from the mentoring of left guard Josh Sitton, who signed with the Dolphins this year.
Buffalo: Linebacker Matt Milano. Milano is starting alongside first-round pick Tremaine Edmunds in essentially a two-linebacker defensive formation. A fifth-round pick in 2017, Milano was eased into the starting lineup and finished with five starts. This year, he's has started all nine games, credited with 55 tackles.
N.Y. Jets: Linebacker Darron Lee. Lee was their first-round pick out of Ohio State in 2016 and has been slow to live up to his lofty draft status. He finished second on the team in tackles each of his first two seasons, but big-time impact plays were missing for a middle linebacker. He's off to the best start of his career as a more consistent playmaker.
Houston: Defensive back Kareem Jackson. Jackson had a bad 2017 at cornerback, but has played both cornerback and safety this season and has been strong in a secondary that has dealt with numerous injuries.
Tennessee: Linebacker Jayon Brown. A fifth-round pick out of UCLA in 2017, the second-year linebacker is leading the Titans both in total tackles and with four sacks. The speedy Brown has started three of eight games this season and has been a key piece of a defense currently allowing the fewest points in the NFL.
Jacksonville: Kicker Josh Lambo. Lambo has made a team-record 23 consecutive field goals in the regular season, including a career-best 57-yarder in London. He had made 27 in a row, including the playoffs, and all 12 of his extra points in 2018.
Indianapolis: Quarterback Andrew Luck. Luck didn't just miss all 16 games last season but 26 of 45 overall because of various injuries (shoulder, lacerated kidney, concussion and then shoulder again). Luck has completed 65.8 percent of his passes, is second in TD passes (23) and is on pace to top 4,000 yards again.
Pittsburgh: Running back James Conner. Conner has seamlessly replaced Le'Veon Bell with four games with at least 100 rushing yards, 50 receiving yards and at least one touchdown, the most such games by a player in a single season in NFL history. Conner has 1,085 scrimmage yards (706 rushing, 379 receiving) and 10 total touchdowns (nine rushing, one receiving).
Cincinnati: Wide receiver Tyler Boyd. Boyd has been a solid complement to star A.J. Green. He has 49 catches for 620 yards and five TDs and will be counted on in the second half with Green dealing with a toe injury.
Baltimore: Quarterback Joe Flacco. Despite his team's recent slump, Flacco has done well for the Ravens. He's got 12 TDs, six interceptions, 2,465 yards passing and an 84.15 QB rating. Last year, Flacco finished at 18 TDs, 13 INTs and 80.4. He had 3,141 yards.
Cleveland: Defensive tackle Larry Ogunjobi. Ogunjobi, a third-round pick in 2017, made one start as a rookie. The 6-foot-3, 305-pounder has developed into a stout run stopper. He also has quickness to get to the quarterback. His presence inside has forced teams to adjust their blocking schemes and given Myles Garrett some favorable one-on-one matchups.
Kansas City: Quarterback Pat Mahomes. Mahomes started Week 17 last year, but in his first full season as No. 1 QB he's breaking records all over the place. Mahomes, who appeared in his 10th career game last Sunday against Cleveland, has 29 touchdown passes and 3,185 passing yards, both the most by a player in his first 10 games.
L.A. Chargers: Running back Austin Ekeler. The second-year player, an undrafted free agent, is averaging 5.8 yards per carry and 12 yards a reception. Ekeler has teamed with Melvin Gordon to form one of the league's top running back duos.
Denver: Wide receiver Emmanuel Sanders. He was hurt most of 2017 and caught two TD passes, both in Week 2 vs Cowboys. Last year, he had 47 catches for 555 yards in 12 games. This year, he has 56 catches for 707 yards and three TDs and even threw for a TD, hitting fellow SMU alum Courtland Sutton vs. Arizona.
Oakland: Running back Jalen Richard. Richard showed flashes his first two seasons as an undrafted free agent out of Southern Mississippi, but has emerged as a key part of coach Jon Gruden's offense.
Washington: Safety D.J. Swearinger. Swearinger is tied for the NFL lead with four interceptions as a key part of a secondary that has Washington in first place.
Philadelphia: Running back Wendell Smallwood. Smallwood has a career-best 400 scrimmage yards (257 rushing, 143 receiving) along with one rushing TD and two receiving TDs after only playing eight games last year when he was inactive often.
Dallas: Linebacker Jaylon Smith. The former Notre Dame standout is finally showing his college form almost three years removed from a devastating left knee injury in his final game for the Irish.
N.Y. Giants: Wide receiver Sterling Shepard. Shepard has 40 catches for 542 yards and two touchdowns. Despite a porous offensive line, he is on pace for career highs.
New Orleans: Defensive tackle Sheldon Rankins. Rankins was a 2016 first-rounder who missed the first half of his rookie season with a leg injury. Last season, he was solid, but highlights were few. Through the first eight games, Rankins has four sacks and 21 total tackles, on pace for considerable increases in those categories.
Carolina: Defensive tackle Kyle Love. Love is a backup, but is making some outstanding plays in the middle of the line, including a forced fumble in Week 8 against Ravens RB Alex Collins that led to a TD and helped turn the game.
Atlanta: Free safety Damontae Kazee. Kazee is tied for the NFL lead with four interceptions. He was forced into a starting role after Keanu Neal and Ricardo Allen were placed on IR.
Tampa Bay: Tight end O.J. Howard. The Bucs attribute Howard's growth to being in his second year, being more comfortable with the playbook and the offense in general. He has caught three touchdown passes in the past two games.
Chicago: Quarterback Mitchell Trubisky. Trubisky has a 96.1 passer rating, 64.6 percent completion rate, 16 touchdown passes, seven interceptions and a 5-3 record. Last year, he had a 77.5 rating, 59.4 percent completion rate, seven TD passes, seven interceptions and a 4-8 record.
Minnesota: Defensive end Stephen Weatherly. Weatherly was a seventh-round draft pick in 2016 who spent most of the season on the practice squad and mostly was on special teams in 2017. But when Everson Griffen was sidelined, Weatherly moved into the starting lineup and had seven tackles, two quarterback hits and one sack in his first career start against the Bills.
Green Bay: Defensive lineman Kenny Clark. Clark, playing in his first-year of coordinator Mike Pettine's system, already has four sacks in seven games, nearly equaling his output (4½) last year.
Detroit: Wide receiver Kenny Golladay. Golladay has surpassed his rookie season production and that allowed the Lions to trade Golden Tate to the Eagles at the deadline. He has 33 receptions for 523 yards and three touchdowns.
L.A. Rams: Linebacker Cory Littleton. After two years as a backup linebacker and special teams guy, Littleton, an undrafted free agent, earned the starting job when Alec Ogletree was traded in the offseason.
Seattle: Running back Chris Carson. Carson showed flashes last year before getting hurt, but the combo of a better offensive line and a new running scheme has fully displayed his skills.
Arizona: Safety Budda Baker. Baker has made a big impact after having his role greatly expanded after being a first-team All-Pro on special teams as a rookie. Now he's a significant part of the regular defense, not just a special teams ace.
San Francisco: Tight end George Kittle. Kittle was a pleasant surprise as a fifth-round pick last year with 43 catches for 515 yards after being mostly used as a blocker at Iowa. He now is one of the game's most well-rounded tight ends. He ranks third at the position with 41 catches and second with 692 yards and is a powerful blocker in the run game.