Every team has a host of star players who provide the cream on top of a fine group performance.
And then there's that one player who holds the key to his club's fortunes, whose absence when sides are picked makes fans tremble in trepidation.
AFL.com.au reporters have taken on the task of nominating each club's most critical player. Do you agree with our assessment?
Rory Sloane is the heart and soul of the Crows. The reigning Malcolm Blight medallist is a contested-ball animal, able to extract the Sherrin from stoppages and get it moving forward. But it's his pressure acts and defensive running that set him apart from the field. Sloane's one-game suspension for the round 23 clash with West Coast proved costly. With a top-two spot on the line, the Crows couldn't cover his absence, lost the game and eventually bowed out in the second week of the finals to Sydney at the SCG. With Sloane, the Crows can win the premiership. Without him, they would be lucky to make the top four. - Lee Gaskin
The horrors of last year compared with the early-season promise can be put down to a number of things, not least the health of new skipper Dayne Beams. The star midfielder played just two games in 2016 because of persistent knee problems, and after a slightly interrupted pre-season has started this year on fire. Not only is his inside grunt a huge help to Tom Rockliff and company, but his outside class is something the Lions have been begging for. They look a more polished and composed unit with Beams in the middle. With youthful key position players at both ends, they can cover injuries in most places and not lose much, but a full season from Beams would make a world of difference. - Michael Whiting
In the absence of Andrew Phillips, Matthew Kreuzer carries a huge responsibility in the ruck, and in the three games this year he has been most impressive. Finally his battles with injury are behind him and he is playing to the level that the Blues hoped for when they took him as the No.1 selection in the 2007 NAB AFL Draft. The ruckman, who is an unrestricted free agent at the end of this season, has averaged 30 hit-outs a game and is in the top five at Carlton for contested possessions, clearances, tackles and inside 50s. Importantly, he has booted three goals straight. - Howard Kotton
Matthew Kreuzer celebrates the Blues' win over traditional rivals Essendon. Picture: AFL Photos
The Pies' Achilles heel is their leaky defence, and in particular their shortage of quality key defenders, so the importance of premiership and All Australian centre half-back Ben Reid cannot be understated. If the 'Woods lost the consistent, strong-marking left-footer, it's likely the dam wall would be irreparably broken, and they'd be forced to call up former Demons veteran Lynden Dunn or perhaps Lachie Keeffe, or even make do with admirable undersized options Tyson Goldsack and Jeremy Howe. Brodie Grundy would also be difficult to replace given the Pies are light on for ruckmen, and they can ill afford to lose skipper Scott Pendlebury, whose absence would potentially leave a gaping leadership void. - Ben Collins
There are a few options here for the Bombers given some of their midfield stars and Joe Daniher's importance in attack. But Michael Hurley would be very close to the top of John Worsfold's list. Hurley is the Bombers' most valuable defender, he takes on the opposition's leading forward while also creating rebound, and his tough, uncompromising approach sets a standard for his team. The Bombers do have some depth in defence, but not of Hurley's quality. The Bombers could always swing Cale Hooker back if Hurley went down with injury, but that would have repercussions for the forward-line structure too. - Callum Twomey
You could mount a strong argument for Aaron Sandilands, but it's impossible to go past the 2015 Brownlow medallist and new skipper Nat Fyfe – especially after his heroics in dragging Fremantle over the line against the Western Bulldogs. Fyfe's herculean final quarter – including 12 touches, eight of which were contested – was pivotal in the Dockers clawing their way back from a 14-point deficit and his teammates walk taller with him in the side. When Fyfe dominated the first half of 2015, the Dockers looked genuine premiership material. His absence after round five last season due to a broken leg was a hammer blow with Sandilands already sidelined by broken ribs, and it's no coincidence Freo's season slid into the abyss. - Travis King
The most prolific Cats aren't necessarily the ones they can't afford to lose. If one of Patrick Dangerfield or Joel Selwood went down, the other – plus the likes of Mitch Duncan, Cam Guthrie and Sam Menegola – are still there. But, they just don't have another player like power forward Tom Hawkins. The 28-year-old leads their goalkicking with 12 from Daniel Menzel (10), and while the team is less reliant on Hawkins than in the past, the 198cm, 110kg forward takes the biggest defender each week and is a strong contested marking target for his midfielders to spot. – Jennifer Phelan
The Suns have some of the best key-position players in the competition, but it's also the area in which they are most vulnerable. They could ill afford to lose either co-captain Steven May or Tom Lynch, but an absence from May would be particularly harmful. Last year he was suspended for five matches and the Suns spiralled to an average losing margin of 80 points (although they were also in the middle of a midfield injury crisis). Aside from trusty sidekick Rory Thompson, there is precious little depth in the key defensive posts, with youngster Jack Leslie and versatile Keegan Brooksby the only alternatives. An injury to All Australian Lynch would also be a huge blow, but coach Rodney Eade has previously shown he can conjure magic from small forward lines. - Michael Whiting
Tom Lynch and Steven May are crucial to the Suns' leadership. Picture: AFL Photos
The Giants' list is stacked with talent and depth but star ruckman Shane Mumford remains the one man they can't afford to lose. The emerging Rory Lobb does a solid job giving the big man a chop-out during games but he's still learning the craft, Dawson Simpson doesn't have the mobility to play regularly at senior level, and Tom Downie is on the long-term injury list while he deals with some mental health issues. Mumford's aggressive nature and physical presence sets the tone for the side and his importance goes well beyond the stats sheet. - Adam Curley
Not a lot is going right for the once-mighty Hawks, so it would be just their luck if ex-Sydney Swan Tom Mitchell was forced to miss time. Mitchell, one of the men brought in to reinvent a midfield sans Jordan Lewis and Sam Mitchell, has easily been Hawthorn's best player through the first three rounds, averaging 34 disposals and more than six tackles per game. That impressive output has not saved the Hawks from an 0-3 start, but imagine how dire the situation would be if he wasn't there to carry such a heavy on-ball load. - Marc McGowan
Read: Cohesion the key, says Tom
Melbourne's worst fears have been realised with All Australian ruckman Max Gawn to be sidelined for up to three months because of a significant hamstring injury. Gawn had surgery on Tuesday after hurting his right hamstring in the Demons' 29-point loss to Geelong. Starting this week against Fremantle and Aaron Sandilands (No.1 in the AFL for hit-outs), Melbourne will now have to start rolling out its contingency ruck plans. Back-up big man Jake Spencer is likely to get the call up in Gawn's place, with the Demons now considering how best to set up their midfield in Gawn's absence. Melbourne is equal-third in the competition in centre clearances, thanks largely to Gawn's influence, and his ability to give midfielders Nathan Jones, Clayton Oliver and Jack Viney first use out of the centre is a crucial element of the Demons' game plan. - Ben Guthrie
The Roos have already shown, to varying degrees, they can cope without Jarrad Waite (replaced by Ben Brown) and Todd Goldstein (Braydon Preuss). But could they do the same if key defender Robbie Tarrant went down for an extended length of time? Tarrant, the 2016 club champion, provides genuine height at 196cm, with the undersized-but-dogged Scott Thompson and kids beside and underneath him. He has repeatedly proven himself capable of manning the competition's gorillas, and that would become a serious problem area if his history of injuries repeated. It might be worth Brad Scott persisting with last week's first-gamer Sam Durdin just in case the scenario presents. - Marc McGowan
Key defender Robbie Tarrant is the Kangaroos' 2016 best and fairest. Picture: AFL Photos
Ollie Wines has taken the mantle as the Power's best player, but the emergence of Sam Powell-Pepper and Brad Ebert's return to an inside midfield role means they have back-up in that department. You can't say the same about the key forward position. Charlie Dixon is crucial to the Power's attacking structure. Even if he's not kicking goals himself, Dixon brings the ball to ground and presents a contest so his small forwards can pick up the scraps. If Dixon is unavailable, the Power will have to rely on 27-year-old rookie Brett Eddy, raw draftee Todd Marshall, utility Jackson Trengove or take Patrick Ryder out of the ruck. - Lee Gaskin
The Tigers may have increased their midfield depth and ability to cover injuries there if need be, but Dustin Martin is in a different class. Damien Hardwick's willingness to send him forward for periods and isolate him 25m ahead of the ball has been a feature of the Tigers' play and an element they can't afford to lose. Martin has won 22 per cent of his possessions inside 50 this year, compared to eight per cent in 2016. He has also been involved in 35.4 per cent of Richmond's scores this season (ranked No.1 at the club). He hasn't lost a one-on-one contest, neutralising them at worst, and he is averaging a career-best 32.7 possessions (No.4 in the AFL), despite his increased time forward. The Tigers might be able to cover him in the midfield and get by, but they can't forward of centre. - Nathan Schmook
This is a tough decision but the answer is probably Jack Steven, narrowly over Nick Riewoldt. There's a reason Steven has won three of the last four Trevor Barker Awards. His work inside the contest is obvious to anyone who watches Saints games, but his burst out of stoppages is what makes him a star of the competition. Steven's absence was felt against the Brisbane Lions last week, when St Kilda lacked star power in its midfield. While Riewoldt's best-on-ground effort in that match underlined his importance, the club is well stocked for forward targets and is better equipped to handle the former skipper's absence than Steven's. - Dinny Navaratnam
The Swans have an elite midfield unit but there's no doubt skipper Josh Kennedy is the main man in the middle. The three-time club champion and All Australian is the contested ball and clearance king in Sydney, and has played 23+ games in all six of his years at the Swans, showing how consistent he is as the linchpin of John Longmire's onball division. Luke Parker, Dan Hannebery and Kieren Jack are also stars, and Isaac Heeney is coming of age, but without Kennedy, the team loses its most reliable ball winner and stoppage specialist. - Adam Curley
Many would have said the Eagles couldn't afford to lose spring-heeled ruckman Nic Naitanui if they were to stay in the premiership hunt, but time will tell if that's the case. The addition of Hawthorn champion Sam Mitchell has somewhat softened that midfield blow. However, if dual Coleman medallist Josh Kennedy went down the Eagles' flag hopes would hang by a thread. The gun full-forward has booted 162 goals in the past two seasons and when he fires West Coast rarely loses. The Eagles have only been beaten once in 18 games since the start of 2015 when Kennedy has kicked at least four goals. - Travis King
The Eagles can't afford to lose star forward Josh Kennedy. Picture: AFL Photos 
While he's the Bulldogs' best player, Marcus Bontempelli is also their most important. At 21, the midfielder is already an elite player in the competition, with his all-round game impossible to stop at times. He's ranked third at the Dogs this season for disposals (76), equal second for goals (five) and fourth in tackles (17). A snapshot of the reigning best and fairest's importance was when he more or less dragged his side across the line against Sydney in round two. Versatile big man Tom Boyd hasn't recaptured the form this year that saw him one of the best in the Dogs' premiership triumph, but he's still critical to Luke Beveridge's set up with No.1 ruckman Jordan Roughead sidelined through injury. - Ryan Davidson
