Richmond have officially added Western Australian youngster Sydney Stack to their list after lodging the paperwork on Monday.

The 18-year old has been training with the Tigers since December as the club decided whether to sign the exciting midfielder under the pre-season supplementary rules.

After performing strongly at last year's National Carnival, Stack was widely considered one of the best prospects the 2018 draft but was not picked up due to off-field issues.

Tigers footy boos Neil Balme was delighted to secure Stack's future at the club after training strongly over the pre-season.

“We’re delighted to welcome Sydney to the club, he’s worked really hard to secure a spot on the list, and we know he’ll continue to work hard to develop his football,” Balme told the club website.

“Sydney’s got great speed, skill, and competes really hard, so we’re excited by what he’ll bring to the team.

“We think that Richmond is a positive environment for him, and we’re pleased with how he’s settling into the Club and our football program.”

Stack joins ex-Saint Maverick Weller to join Punt Road via the new rookie rules.