The launch of the Official AFL Player Ratings, brought to you by Vero, has added a whole new dimension to this weekend's action on the field.

In round eight, some of the highest-rated players will be going head-to-head, while many players have the chance to dramatically improve their ratings with good performances.

On the flipside, a number of players will need to be near their best or they will slide down the pecking order when the updated ratings are released on Monday, May 20.

Key match-ups this weekend
It's shaping up as an intriguing battle of the big men when West Coast meets North Melbourne at Patersons Stadium on Friday night. Eagles star Nic Naitanui remains the No. 1 ruckman in the competition, despite missing a number of games at the start of the season. He'll take on Todd Goldstein, whose solid form so far this year has consolidated his position as the No. 3-rated ruckman in the league (St Kilda's Ben McEvoy is No. 2). Goldstein earned 26.6 points in the win over the Western Bulldogs last weekend, which was the fifth-best score of round seven.

Two of the best midfielders will cross paths when Collingwood takes on Geelong at the MCG on Saturday night. Cats skipper Joel Selwood is currently No. 3 in the overall standings, behind Gold Coast captain Gary Ablett and Sydney Swans gun Josh Kennedy, while Magpies star Scott Pendlebury is No. 5.

Players on the up
Fremantle forward Michael Walters leapt 32 places, from 662 to 634, after picking up 19 disposals and kicking four goals against Collingwood last weekend. Walters is averaging 16 possessions and almost three goals per game this season.

Players who need to lift
Collingwood defender Jordan Russell needs to hold his place in the Magpies' line-up or he will continue to fall down the ratings ladder. Russell fell 24 places last week, from 426 to 450. Russell, who missed the Pies' round six and round seven games, has been recalled for the crucial clash against Geelong on Saturday night, so at least he has the chance to build on his points tally this weekend.

Twitter chatter
There's been plenty of talk in the Twitterverse about why Fremantle's Luke McPharlin is No. 288 in the overall ratings and is just the 77th-best defender. @Wigarus, tweeted: "How do you justify McPharlin's ranking?"

The thing about McPharlin is that although he averages a touch over 15 possessions per game, which is not bad for a key defender, his direct involvement in passages of play that lead to Fremantle scores is not particularly high.

The Official AFL Player Ratings is weighted towards players who directly help their team score. When the concept was being developed, a number of different algorithms were trialled, including one in which more weighting was given to defensive acts like spoils. The issue was that Jack Redden from the Brisbane Lions became a top-10 player under such an algorithm, which just didn't seem right.

Keep in mind that although the Official AFL Player Ratings only recently went live on AFL.com.au, Champion Data has been collecting the requisite information since 2007.