Sydney - Each season brings with it new referees and Waratahs coaches Michael Cheika and Daryl Gibson are learning the hard way about the priorities of this year's crop.

The Waratahs were given a yellow card for repeated infringements in the tackle area against the Rebels on Friday, prompting Cheika to voice his disappointment about the carding and Gibson to concede the team was getting it wrong at the breakdown.

Both said they needed to be more mindful of the power of interpretation in the highly contested contact area but also made it known they were baffled after two games under two different referees.

VIDEO: Waratahs v Rebels - highlights

''The Australian teams are very competitive at the breakdown and that's something referees are going to have come up to speed with,'' Gibson said. ''The Reds, Brumbies and Waratahs are all very competitive around that area and are putting the refs under pressure to get that right.''

It's a well-timed nudge before a crucial derby against the Brumbies in Canberra next weekend. The game will feature David Pocock and Michael Hooper, two of the best fetchers in the world, going head to head in a game that will help to shape the Australian conference.

The Waratahs will be keen to strike the right balance to avoid a repeat of Friday's game, in which, halfway through the first half, new referee Rohan Hoffman warned captain Dave Dennis that they were pushing the boundaries. Hoffman pulled the yellow card from his pocket less than five minutes later after penalising hooker Tatafu Polota-Nau for not rolling away in a tackle on Rebels halfback Nick Phipps.

Cheika disagreed with the call.

''I was really disappointed about the yellow card from the referee because it [was] a collapsed maul and the player doesn't have to go anywhere,'' he said. ''But I understand it's also Rohan's first game of Super Rugby so, like anyone else, [he is] getting acclimatised.''

Dennis said the Tahs were awarded a penalty for the same thing in the 73rd minute.

While the coaching staff work on the technical aspect of the breakdown, there will also be fascinating selection discussions. Cheika has gone with a forward-heavy, five-two bench for the past two matches, leaving rookie Ben Volavola to plug holes in the back line.

Volavola was outstanding when he replaced winger Tom Kingston in the second half, with the substitution forcing fullback Israel Folau to the wing while Volavola stepped in at the back.

Cheika said Folau was ''a lot more efficient'' after the switch, while Gibson said Volavola's impact was in distribution. Referring to the balance on the bench, Gibson said: ''We recognise that where we needed our strength to be in the last two rounds was in the forwards.''