STARTING on-field for the opening bounce is a concept foreign to Hawthorn forward Luke Breust.

The 20-year-old former rookie has been the Hawks' starting substitute player in all four of his senior games since his round eight debut against St Kilda.

He knows exactly what it's like to have to temper your enthusiasm so you don't exhaust yourself on the bench before you come on, and what you should do when you enter the arena when the tempo of the game is at its peak.

He's had it all, really. He played nearly a full game against the Saints after Stephen Gilham injured his knee early in the first quarter.

Then, he only got a quarter the following week against the Sydney Swans, which was increased the next round against the Western Bulldogs when he replaced Chance Bateman - who injured his ankle - for the start of the second quarter.

On Sunday against Fremantle, he wasn't called upon until the middle of the third when he came on for Jordan Lisle, who struggled with accuracy in his first AFL game.

It was a move that proved a success on both fronts. Breust made his biggest impact so far with three goals - two of which were in the match-defining fourth quarter - and Fremantle battled to match the Hawks' run having gone in with a tall line-up, said Alastair Clarkson afterwards.

In turn, Fremantle's substitute player - Rhys Palmer - was deployed into the game in the fourth quarter and had just two touches.

"I find it all right to come on in the middle of the third term, even when the game is hot," Breust told hawthornfc.com.au after the game.

"I just try and get out there and run my opponent around and hopefully get on the end of a few and have an impact when I get on."

On top of the knowledge added from another senior match, Clarkson said Breust’s strong influence on the result would be telling in his development.

Breust said there was no definitive reason why he had been used as the green-vest man for the past month, and it was "just the way it's worked out".

So, what's the best part about starting the game as a sub?

"The run in the players' legs is gone a little bit so you do feel fresh and pretty quick," Breust said.

"It's also still working out that I'm still getting good minutes on the field even though I'm starting as a sub.

"I just try and come on and make an impact and play my role."

And the worst?

"The week I played against Sydney, only playing a quarter, I had to do a top-up session on the Monday, maybe just a 25-minute threshold run, to make sure your match fitness holds up," he said.

"This week, I'm not sure. I'll let the fitness staff make that call. I've played just over a quarter so there might be a bit of running."