That decision-making theory says decisions are assessed on the eventual outcome rather than by taking into account the information or perspective available at decision time.
The theory is relevant to the questions surrounding Primus's decision to allow Collingwood's Harry O'Brien to play as a spare in defence on Saturday.
The decision looked worse than it was because Port Adelaide lost the game with O'Brien running loose. Therefore whether or not leaving O'Brien alone was the main cause of the loss became less relevant.
Going into the game, most would have agreed Port Adelaide could exploit its height advantage up forward if it generated enough inside 50s. If you accept that premise, then Primus's calls start to make sense.
In the previous two games, Port had managed 84 inside 50s compared to the opposition's 116 inside 5os, so Primus identified the midfield as an area that needed to improve. "We needed to create some more of the ball and I thought playing a spare (in the midfield) got us back in the game," Primus said.
Port Adelaide initially chose to position its spare around the ball. In the first half at centre bounces, Kane Cornes came off the wing free of a direct opponent. At stoppages, whichever player spilled out as an extra gave support. Collingwood made sure it was not Danyle Pearce.
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The effect was as the Port coach hoped, with Port Adelaide recording 55 inside 50s to the Magpies' 47.
However, Port's forwards did not come to the party, only taking nine marks inside 50. Post-game, disappointed Primus bemoaned Port's lack of marking power inside 50.
In contrast, the Magpies' 47 inside 50s were of a higher quality, because they were often allowed to run through the midfield free of pressure.
After the defeat Primus was asked the legitimate question as to why he made such a call in relation to O'Brien. While he answered, it was clear he did not think it was a bad decision nor the main cause of the loss.
The defence he raised can be summarised in three points:
1. Collingwood's goals in the first quarter were not generated from O'Brien.
2. Port Adelaide needed to bolster numbers around stoppages to get the ball inside 50 to give itself a winning chance.
3. Lack of pressure was the biggest problem.
The statistics back Primus up on his first point. Collingwood started three scoring chains from its defensive 50 in that quarter that ended in scores. None came via O'Brien. He was part of one scoring transition in that quarter when he bounded through the centre as the Magpies ran the ball from defence.
In the end only four of O'Brien's 29 possessions were part of scoring chains, two of the scores launched from intercept possessions.
Throughout the game the Magpies started 44 chains of possession from its defensive 50. Only five (two goals, three behinds) ended in scores.
The real danger, as Primus noted, was coming from centre clearances and rebounds from the defensive part of the midfield. Collingwood kicked three goals from centre clearances and four goals, three behinds from chains of possession generated in the back half of the midfield.
Port Adelaide's players did not make use of the extra number in that part of the ground. They did not tackle hard enough or exert enough pressure to stop Collingwood making quick entries inside 50. With the lowest tackling numbers in the competition, it is an area Port need to address.
The question difficult to answer is what effect O'Brien's presence had regardless of statistics. It's a question Primus might want to ponder.
O'Brien was running interference, blocking space, forcing the Port defenders to look twice before kicking and be more precise. Some of the terrible rebounding from Port could possibly be explained by the uncertainty O'Brien's presence caused.
The players will be able to tell Primus the effect a spare defender had on the way they played.
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O'Brien's role also added energy to the team. His Magpie teammates could run out of defence and spread with confidence because they knew they had an extra man who could cover for them if the ball was turned over. O'Brien's flexibility meant he was a more than handy back-up.
His teammates could go for marks knowing they had an extra crumber at the fall of the football too. Collingwood defenders took 10 intercept marks in their defensive 50. O'Brien was also instrumental in positioning himself in front of the Port Adelaide forwards and halting their leap. He could do so himself knowing he did not have to worry about his opponent crumbing.
All this was made possible because Collingwood's midfielders exerted more pressure than Port Adelaide.
Statistics suggest Cornes played his role for Port Adelaide reasonably well: 37 disposals with eight involved in scoring chains. He put the ball inside 50 five times and won three clearances but the forwards could not capitalise.
So his effect became much less obvious to watchers than the mop-up role O'Brien was playing.
All that was left then was for the outcome bias to work its wonder.
And Primus's decision would look worse than it was.
Stats supplied by Champion Data
The views in this article are those of the author and not necessarily those of the AFL or its clubs
