SHADOWING Dane Rampe for the better part of seven months has helped Sydney's Tom McCartin become a rock in their AFL defence.

McCartin was drafted in 2017 as a mobile forward with a reputation for clutching contested marks.

But he will likely be manning Ben King in Saturday's clash with Gold Coast at Metricon Stadium, having repeatedly taken the opposition's most potent key forward this season.

McCartin had predominantly served as a forward until round 14 of Sydney's injury-cursed 2020 season.

Tom McCartin of the Swans is tackled by Alec Waterman of the Bombers during round four, 2021. Picture: AFL Photos

Coach John Longmire reshuffled his magnets at halftime of that clash with Port Adelaide, shifting McCartin into the backline as Aliir Aliir entered the ruck.

"It was just incidental," McCartin said of what proved a coaching masterstroke.

"I felt pretty comfortable down there, played there for the rest of that season and stayed there.

"Still learning every week but really enjoying it."

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Longmire knows the upside of having experience in both 50m arcs, having himself played at fullback in 1989 and then winning the Coleman Medal a year later at age 19.

"It helps you in both positions," McCartin said, having ranked sixth in the league for intercepts across the opening five rounds of 2021.

"I know what forwards hate.

"I'm always trying to think like that 'what is the forward trying to do' and how do I stop that."

Dane Rampe of the Swans celebrates a win in round four, 2021. Picture: AFL Photos

McCartin impressed on Power forward Charlie Dixon last year, while holding his own in a final-round tussle with Coleman medallist Tom Hawkins was perhaps the greatest sign yet he could become a reliable key defender.

Aliir was then traded to Port, leaving a void that may have proven immense if not for McCartin.

He highlighted the mentorship of injured co-captain Rampe as being pivotal in his development.

"All the little things that make Dane a great defender, I'm just trying to pick up," the 21-year-old said.

"He's been really good for me. He's a great leader, his physical prep is unreal and so is his opposition analysis."

Paddy McCartin with Sydney's VFL team during a practice game in 2021. Picture:

One notable difference to last year has been the arrival of McCartin's older brother Paddy, who shifted to Sydney to play with the Swans' reserves in a bid to reignite his AFL career after repeated concussions.

"I watched most of it (Paddy's round-one game)," Tom McCartin said.

"It's just good to see him enjoying himself and having fun, that's the main thing.

"Hopefully it all works out for him."

McCartin briefly returned to his first craft in Sydney's derby defeat, when an attempted match-winning goal from beyond 60 metres fell short after the final siren.

"I was hoping it'd be a Malcolm Blight torp. I'll keep practising," he said.