Brodie Smith - Injury has held Smith back so far this season but he's still shown how important he is to the Crows' structure. Coach Phil Walsh wants his side to play a kicking-dominated style of football, and as one of the club's best field-kicks Smith's skills are crucial. Last season the half-back flanker led the Crows for rebound 50s (second in the competition) whereas this season others have picked up the slack. Rory Laird has lifted his game and prior to his knee injury Matthew Jaensch was a rebounding dynamo. Smith's focus was pushed higher up the ground and he's now second at the club for inside 50s. Smith's brilliant right foot allows him to become a playmaker and, although two concussions have limited his output this year, his influence on results will only increase in the second half of the season. - Harry Thring

Pearce Hanley - Daniel Rich used to be the Lions' barometer for success, but over the past two or three seasons, they have shown on numerous occasions an ability to win without much impact from the blonde left-footer. Hanley is a different story, though. Since 2012 – when the classy Irishman really established himself as a bona fide AFL player – the Lions have a 15-6 win-loss record when Hanley kicks a goal. Long regarded alongside Rich as the best ball user at the club, Hanley is most damaging when he's creating havoc forward of centre. After not playing the first 10 rounds in 2015, the 26-year-old is now back on deck and ready to impact the second half of the season for Justin Leppitsch's men. - Michael Whiting

Bryce Gibbs - As he showed in his best and fairest winning season last year, Gibbs is capable of brilliance. But there has been precious little of this on display this season as the Blues’ on-field fortunes have plummeted. When he was on last season you could guarantee the Blues would be competitive at the very least. Gibbs' struggles this year have mirrored the team. Last year he was 10th in the AFL for clearances for the home and away season (5.6 a game), but this season his average has dropped to 4.9 (equal 54th overall). Gibbs has missed the Blues’ past two games with a back complaint but his numbers in several key categories have fallen significantly from 2014 – notably average disposals (24.8 to 21) and kicking efficiency (59.4% to 48.4%). The rise in tackles (4.9 in 2014 up to 5.5 this season) is the only statistic to buck the trend. - Howard Kotton

Jamie Elliott - If you can keep Jamie Elliott goalless, you are well on the way to beating Collingwood. The problem is it's rare for the brilliant goalsneak not to hit the scoreboard. This year Elliott has failed to kick a goal just twice, and both times the opposition (Adelaide and Geelong) won the midfield battle decisively, thus limiting his opportunities. In Collingwood's only other loss, the livewire small forward was held to just five kicks (a two-year low when playing a full game) and two goals against Richmond. In 11 games this year Elliott has tallied 25.8, including seven multiple-goal efforts, and it seems only injury will prevent him from surpassing his previous-best effort of 33 majors from 17 outings last year. The 22-year-old matchwinner is developing a cult following among Pies fans, and it's little wonder given he has so many tricks. He can accumulate goals from various sources – big marks, marks on the lead, crumbing and classy link-up play. Elliott is also difficult to keep out of the action because he is a fierce, brave competitor with speed and improving endurance, enabling him to help out in defence one moment and be on the end of the play the next. And it's not only the goals Elliott kicks himself – he has been credited with 12 goal assists (equal-seventh in the AFL), including a career-high three in the win over the Giants on Sunday. - Ben Collins

Jason Winderlich - Winderlich has missed plenty of footy throughout his career due to injury, but when he is in the line-up he has the ability to change the dynamic of a game. His speed, class and smarts give him a mix near goal that is rare at Essendon, and he is able to set up opportunities as well as convert his own. Winderlich isn't Essendon's best player or its most important, but he can spark the Bombers and in 16 games last year he kicked 15 goals. The year before he slotted 17 from 12 appearances. Captain Jobe Watson and midfield partner Dyson Heppell play well most weeks, but Winderlich's absence this year with a back injury has cost the club some vital pace and finish. He is expected to return to Essendon's senior line-up after its bye having played two VFL games since recovering from his back injury, which limited him over summer. - Callum Twomey

Hayden Ballantyne - He is not a leader in many of the 'in vogue' statistical categories, but goals are the most important stat in the game and Ballantyne's importance to Fremantle is measured by his scoreboard influence. He has kicked three goals or more 31 times in his AFL career and the Dockers have won 30 of those matches. The only loss was in his second game in 2009, a season when the Dockers finished 14th. If he hits the scoreboard, the Dockers win. Ironically, given Freo's fast start this year, Ballantyne has only kicked eight goals in 2015. He has not kicked more than two in any single game and the Dockers have won 10 of 11. Ross Lyon's men still have had marked improvements in a number of areas and Ballantyne's lack of goals is a great sign for any Fremantle fan in terms of what potential improvements the team could make in the second half of the season. Goals from Ballantyne in the finals will be worth their weight in gold. – Alex Malcolm

Tom Hawkins - When the Cats are really up and going, it is spearhead Hawkins lighting them up. The key forward is yet to reach his peak this season, having missed a game due to a glute complaint, while also being a late withdrawal after the death of his mother earlier in the year. Hawkins has kicked 19 goals from nine games this season, but his three-goal performance from limited opportunities against West Coast in round nine displayed just how potent he can be. To illustrate Hawkins' importance, the Cats score 56 per cent of the time when he is involved in a scoring chain – ranking Hawkins fourth in the competition. The star Cat has also averaged the most contested marks (2.7 per game) of any player in the competition this season. If Hawkins can get rolling – and hit the scoreboard more frequently – in the second half of the year, the Cats will be much better placed to mount their finals charge. - Ben Guthrie

Gary Ablett - You can dig as deep as you want – and the Suns being 5-1 when Tom Lynch kicks four goals or more is compelling – but you can't go past Ablett. Let's disregard Gold Coast's first two seasons when they were largely an under-20 team, and just focus on 2013 onwards. When Ablett has played, they were a respectable 17-21, but when he didn't, that dropped to an abysmal 2-15. That's a 45 per cent win ratio down to 12 per cent when Ablett doesn't play. Drill down a little further and the dual Brownlow medallist's impact is even more profound when he plays in the forward half and kicks goals. When Ablett kicks two goals or more, the Suns are 10-7 over the same period. - Michael Whiting

Shane Mumford - What a blow for the Giants, who are now without arguably their most important player for the rest of 2015. You can roll out the encyclopedia of sporting clichés when it comes to Shane Mumford's importance and value to Greater Western Sydney. Not just the Giants' barometer; he's their heart and soul and spiritual leader, the workhorse that drags the GWS wagon. The Giants have recruited bigger names to the club, like Ryan Griffen and Heath Shaw, but you'd have a hard time finding anyone who has matched Mumford's impact. He played just 17 games for GWS in his debut season last year and won the Kevin Sheedy Medal as the Giants' best and fairest. His second and third efforts at stoppages are phenomenal; Mumford has the fourth most tackles of anyone in the league at over six per match, and they are tackles that pulverize opposition players. Laid a season-high nine against the Adelaide Crows in round eight, and in 2015 his count has been lower than six just twice. Some players can spark their side with individual efforts, but Mumford is more like a shock from an electric chair for the Giants, and he does it weekly. Massive, massive loss. - Adam Curley

Isaac Smith - The 26-year-old speedster has been a super player for the Hawks, averaging 20.3 disposals and five marks a game over his career. He also averages just under a goal a game and, as the celebrations show, he loves kicking goals. This year the emergence of Billy Hartung on the wing has freed up Smith to play further up the ground and so far in 2015 he is averaging 26.9 disposals, seven marks and one goal a game. The Hawks badly needed leg speed when they drafted Smith with their first national draft selection in 2011 and he has delivered in spades. But here's why he is the spark for Hawthorn – when he plays, the Hawks invariably win. He has played 95 matches for Hawthorn so far for 76 wins. That's an 80 per cent success rate. No wonder the bloke is always smiling. – Ashley Browne

Nathan Jones - The skipper could hardly be considered a match-winner given his form has hardly fluctuated for four seasons yet the team has struggled to win. However, the truth is Jones has starred in the team's rare victories and there is an argument that if he didn't play well in those wins the team would not have taken the points. He polled Brownlow votes in eight of Melbourne's 10 wins in the past three seasons and earned the most coaches votes in the team's triumphs this season over Richmond and the Western Bulldogs, as well as two coaches' votes in the win against Gold Coast. A champion in this era for the Demons, he must look forward to the time when wins aren't dependent on such performances. Although he sits at No.87 in the Gatorade AFL Player Ratings he carries a bigger load than most. - Peter Ryan

Jack Ziebell - Although ruckman Todd Goldstein has been far and away North's most consistent performer this season, Ziebell has stood out as the Roo who can drag his team across the line in close games. The midfielder's fierce attack on the ball sets the standard for his teammates. Three of North's five wins this season have been by 16 points or less and Ziebell did much of the midfield heavy lifting in all three. In the round four win over Geelong, he had a team-high eight tackles, while he led the Roos with 11 clearances in both round seven against Essendon and round 10 against West Coast. The Roos vice-captain has also hit the scoreboard when his team has needed him to. Perhaps the most reliable set shot at North, he kicked invaluable last-quarter goals against the Dons and Eagles. It's also worth noting that North lost Ziebell to injury early in round three against Port Adelaide when the Roos lost a nail-biter by eight points. Ziebell's inspirational performance against the Eagles saw North chairman James Brayshaw anoint him as the club's next captain. - Nick Bowen

Jay Schulz - As a full-forward Schulz is obviously reliant on delivery to have any sort of impact on matches of football. But the statistics in 2015 are telling: when Schulz fires the Power win. He's averaged four goals in each of Port's five wins this year and fewer than one in each of their six losses. Last year Schulz averaged almost 2.5 goals a game when the Power lost. Port is also averaging far fewer inside 50s than it did last year, which makes it tougher for Schulz to hit the scoreboard. The club is ranked 11th this year for forward 50 entries (50 a game), whereas in 2014 it was ranked second (56 a game). His teammates have spoken about the confidence they gain from his accuracy in front of goal and when Schulz is in the position to kick majors it signifies Port's functioning game plan. - Harry Thring

Brett Deledio - You need look no further than Deledio as the Tigers' barometer, as it's clear how much they miss his class across half forward when he's not playing. This year alone, the 28-year-old has played in five wins from a possible six games, and didn't appear in three of their four losses to round six. It was a similar story last season, when the Tigers lost a host of games before the mid-season break. Deledio didn't play from rounds three to six, and the Tigers dropped three of four games in that time. When he came back in round seven, their form improved slightly, but when the 2005 NAB AFL Rising Star winner got going in the second half of the season, the team won nine games straight. During that period, Deledio kicked 13 goals and averaged nearly six inside 50s a game, which saw him poll 11 Brownlow medal votes. Ivan Maric and Alex Rance are also highly important to the Tigers' structure but Deledio's influence, maturity and leadership across half forward has proved almost crucial to their success. - Jennifer Phelan

Nick Riewoldt - The inspirational skipper has long been his team's barometer, but even more so now as the Saints rebuild under Alan Richardson. With other avenues to goal in 2015, Riewoldt is lifting the Saints with his work higher up the ground. His marks are the best indicator of this. It's a trend that became more prominent in 2014 when he led the AFL in total marks, and it has continued this season. Riewoldt is ranked No.1 in the AFL for average marks and he has averaged 10.25 marks in their four wins. His influence was highlighted with a team-high four goals and 10 marks against Melbourne in round 11. – Nathan Schmook

Kieren Jack - He doesn't receive the media plaudits as much as some of his big name teammates but that’s just the way Jack likes it. His rugby league upbringing helped make him a star and the perfect choice as the Swans co-captain with Jarrad McVeigh. Jack is ranked seventh for tackles in the league at over six per match in 2015, and loves the work that a lot of onballers shun. Racks up 11 contested possessions per game, which makes him one of the competition's elite inside midfielders. He has laid a season-high 11 tackles twice this year, including in the Swans' thrilling four-point win over Hawthorn in round eight when he also had 13 contested possessions. Not just a fantastic leader with his actions on the field, Jack is a significant driver of the Swans' standards on the training track, and is one of the club's most professional players. When Lewis Jetta wanted to improve his tank a couple of years ago, he chose Jack as the man to shadow across the pre-season. Underrated by those outside the walls of the Swans, but inside the Bloods, there's not many held in higher regard. - Adam Curley

Nic Naitanui - His influence is sometimes hard to measure but it is usually profound. Critics and fans wrote off the Eagles' season when best and fairest winner Eric Mackenzie went down and yet they are 8-3. Matt Priddis has won a best and fairest and a Brownlow in the last two seasons and the Eagles haven't played finals. Josh Kennedy has kicked 60 goals in each of the last two seasons as well. The Eagles have only played finals twice in Naitanui's career and they coincided with his two best years. In 2011, he averaged 19 hit-outs, 10 contested possessions and kicked 18 goals. In 2012, he averaged 25 hit-outs, 10 contested possessions, kicked 24 goals and was named All Australian. Naitanui played just 11 games in 2013 due to injury - he averaged 22 hit-outs, nine contested possessions but only kicked nine goals in 2014 and the Eagles finished ninth. He's averaging 32 hit-outs, nine contested possessions and has kicked nine goals already in 11 games this season. A fit and firing Nic Nat means West Coast is in the hunt. - Alex Malcolm

Bob Murphy - At 32, the first-year skipper is arguably having a career-best season, but that's not the only reason he's the Bulldogs' barometer. His infectious love for the club and game has spread quickly through a young list and it's been a major reason for the team's much improved performances in 2015.  His form across half-back at this stage warrants another All Australian jumper, with Murphy 16th in the League for kicks, eighth for rebound 50s and fifth for running bounces. The 281-game veteran has only dipped under the 20-possession mark four times this season and completes his work with an impressive disposal efficiency of 80 per cent. – Ryan Davidson