Returning stars forced Lachie Ash out of the GIANTS backline but he soon forced his way back into the best 22 by blanketing the best opposition midfielders.

When the GIANTS needed someone to nullify in-form midfielder Darcy Parish in a crunch clash with Essendon in round 19, coach Leon Cameron turned to an emerging half-back who had just been dropped to the VFL.

Ash spent the first half of the season in a familiar role at half-back, averaging 22.5 disposals in 11 matches as part of a young group making the most of their opportunities while Lachie Whitfield, Harry Perryman and Phil Davis were sidelined.

A dip in form at the same time as his experienced teammates were returning from injury forced Ash to be the unused medical sub a couple of times then out of the side for the Sydney Derby in round 18.

But the 20-year-old Ash wouldn't be playing at the lower level for long.

"It was a shock when Leon called me in a couple of days before the Essendon game and said, 'We're thinking about playing you on Darcy Parish, what do you think?'," Ash told AFL.com.au.

"He told me they liked my defensive mindset and that I'd continued to show that in the reserves.

"We've talked about me wanting to play onball in the next couple of years and Leon said this is a way to have a crack now. I just jumped at the opportunity."

Ash restricted Parish to only 15 disposals, still the midfielder's lowest haul for the season and half of the 30.7 he's averaged throughout the year.

Since showing he has the speed, stamina and discipline to run with one of the top onballers in the competition, Ash has also limited the output of Port Adelaide's Travis Boak (season-low 24 disposals) and Richmond's Dion Prestia (22 touches).

Ash was recruited to the GIANTS with pick No.4 in the 2019 NAB AFL Draft as a dashing half-back with clean ball skills but has had to learn quickly in his new midfield role.

"As a defender you spend a lot of time on your off-ball work and position, where you can help your teammates. I feel like I have that 'away from the contest' side of my game in a good place," Ash said.

"A lot of what I've learned has been around the contest. It's more around body work, when to make contact with your opponent, positioning at stoppages and centre bounces.

"The big one for me, when I first played on Parish, was how he moved around the contest. He had really quick feet and constantly worked hard, he'd be the first one to every loose ball to try to outnumber or just help his teammates.

"I probably used to jog around the contest, now I try to get to every contest with real intent."

The smooth-moving Ash looms as suitable match-up for Carlton's Sam Walsh when their teams meet on Saturday night.

With Walsh in the draft class a year ahead of Ash, their paths often crossed in junior football and the young GIANT has kept a close eye on how the Blues' young star plays ever since.

Ash is ready for a close-up view of Walsh's abilities this week.

"I played on 'Walshy' in a Vic Country practice match and I can just remember that he likes to run," Ash said. 

"If I'm given the job I'd just try to get on his back as much as I can and limit his influence away from the contest. That's where he probably does most of his damage, he likes to link up.

"But one of Leon's main messages has been that even if it's a run-with role they still want me to try to get my hands on the footy and test them the other way. That's just another part to learn."