GREATER Western Sydney might have more blue-chip stock than any AFL team in history but Champion Data rates its rookie selection Zac Williams as the AFL's most underrated player.

In the 2017 AFL Prospectus, the 22-year-old is rated elite after a season when he averaged 5.6 ground ball gets and was ranked seventh among general defenders for score involvements.

He also combined for an average 405 metres gained a game, a damaging statistic given his ball use off half-back was rated elite.

However Williams, from Narrandera in New South Wales, was chosen way down the order at pick No.55 in the 2012 NAB AFL Rookie Draft.

Such is the impression he has made on Champion Data, he was ranked equal-second behind Geelong's Brownlow medallist Patrick Dangerfield under a new measurement introduced called relative ratings. 

According to Champion Data, the relative ratings measure takes into account "how a player is performing relative to others in his position at the same age, compared to all other players from 2010 onwards".

Williams is blitzing under that measure with player ratings points that are 74 per cent above the average for a general defender.

He played 22 games in 2016 to lift his total tally of games to 53 games since making his AFL debut in round five, 2013.

He finished seventh in the Giants' best and fairest count despite not being selected in the first two rounds and has benefited from the tutelage of mentor Heath Shaw. 

In assessing Williams in the 2017 AFL Prospectus, Champion Data gets straight to the point, saying simply: "Williams is the most underrated player in the AFL".

Top five players for Relative Ratings in 2016

Name                                      Relative Rating
Patrick Dangerfield                    +77 per cent
Zac Williams                             +74 per cent
Max Gawn                                +74 per cent
Nic Naitanui                              +68 per cent
Marcus Bontempelli                   +68 per cent

Champion Data is the AFL's official stats supplier