Roos said Hall's triple 50m penalty that handed the Hawks a certain goal and moved them 10 points clear 12 minutes into the final stanza swung the momentum and handed the home side the four points.
"I think clearly that was the turning point in the game," a visibly disappointed Roos said after the game.
"You can sit here and we can dream up fictional reasons or we can get to the source of the problem, and that was clearly a massive turning point in the game."
The incident began when Hall handed Jarryd Roughead a 50m penalty for arguing with the umpire in the Swans' goal-square.
He then grabbed Roughead by the neck and slung him to the ground as the ball was moved 50m up the ground, which resulted in a second penalty.
Then, as play was shifted 100m forward, he jostled with Hawthorn players and was penalised a third time for contact against Sam Mitchell, which put Roughead in position to goal.
Roos dragged Hall for the incident and refrained from addressing him straight away, but said his teammates remonstrated with him after the final siren.
He said he didn't expect the club's leadership group to hand Hall a penalty for his indiscretion, but there was no denying his actions cost the Swans the game.
"I wouldn't think [they would act against him] for something like that. It's straight after the game, we've briefly discussed it as a group, but I wouldn't think there would be anything like that," he said.
"The group is disappointed, the coaching staff are disappointed, and I'm sure the fans will be disappointed.
"There's no point in painting a rosy picture about it. Everyone saw what happened."
Roos said it was somewhat surprising to see Hall behave like that, considering his recent form.
"To put it in perspective, I don't think it was anywhere near what he did last time," he said.
"But, it was surprising because he's been in good form and we're doing really well as a team.
"We had the momentum going our way and everything was looking pretty good. We had some players up and going a bit, so it was surprising."
Roos also said he would endeavour to look at each individual 50m penalty to see if any were "an overreaction".
He added Hall's actions could not be justified by any potential frustration caused by his sometimes-controversial treatment by the umpires.
"I don't think so. Today there were a few free kicks, and whether that's been simmering now for however many years he's played, I'm not sure. It's hard to answer that," he said.
"There's clearly some frustration at times when he doesn't get the free kicks he should, and we've addressed that with the umpires' department on many, many occasions.
"I think we're at the stage where we know nothing is going to change and he knows nothing is going to change. You've got to accept the way it is and play accordingly."
He said Hall's future would be discussed in the mid-season break, along with other "out of contract, older players" such as Brett Kirk, Leo Barry, Nick Malceski and Jared Crouch.
