IF THERE'S one last message Hawthorn coach Alastair Clarkson gives his troops before they run out on Friday night against Collingwood, it should be this: watch out for Jaidyn Stephenson.

The Magpies forward is officially one of the AFL's fastest starters – equal with Brisbane midfield jet Lachie Neale at the top of the competition for first-quarter impact.

Last week the 21-year-old booted the first two goals of the game against Essendon, before chipping in with another in the final term.

But that brilliant beginning before fading away is far from a one-off. In Stephenson's 43 games, he has booted 24 of his 69 career goals in opening quarters.

Two of those came in his famous quick start in the 2018 Grand Final against West Coast, when Stephenson, who weeks earlier had been crowned the year's NAB AFL Rising Star, kicked two first-term goals.

The numbers show a clear decline after the first change. In second quarters, Stephenson has booted 15 goals; in third quarters, 13. He finishes a little stronger, kicking 17 goals in final terms.

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Champion Data's AFL Player Ratings system shows an even bigger gulf between the speedy forward's opening terms compared to the rest of his games.

For players who have played a minimum of three games this season, Stephenson ranks equal top with Brownlow Medal favourite Neale for impact in first terms. The pair both rate 6.1 for first quarters under in AFL Player Ratings, ahead of third-placed Nic Naitanui (5.3), with Christian Petracca and Devon Smith tied for fourth (5.1).

The Player Ratings uses the "location of and the result of events to measure a player's performance" – essentially valuing the impact of disposals and other key metrics to get a sense of how players influence games.

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Stephenson has had this knack for a while. He ranks seventh in the AFL since the start of 2019 as having the biggest impact in first quarters (of all players who have played a minimum of 10 games from 2019-20), with the likes of Nat Fyfe, Marcus Bontempelli, Dustin Martin and Neale all among the group above him. 

Stephenson isn't to blame for Collingwood's forward difficulties this season. They have averaged seven goals in their two defeats and a draw, and last week went goalless in the second and third terms against the Bombers.

But the numbers do show a dramatic dip from Stephenson after he emerges from the quarter-time huddle.

As clearly the No.1-ranked Magpie in first quarters (with a Player Ratings number of 6.1), Stephenson is then the 25th-ranked player at the club this season – out of 28 – for second terms (0.5 rating), the 22nd-ranked player for third terms (0.9) and the 17th-ranked player in final quarters (1.3).

Stephenson has booted seven goals for the Pies in three games this year, so clearly is doing his bit inside 50. Collingwood will be hoping he can just do it for a bit longer.