'Wow': Crusaders lock red carded for 'dipless' high shot on Michael Hooper

Crusaders lock Hamish Dalzell was red carded for an awkward high shot on Wallaby captain Michael Hooper at a pivotal moment in the 24-21 loss to the Waratahs in Sydney.

With the Waratahs deep on attack inside the Crusaders' 22, Dalzell clattered into the Waratahs openside as he peeled off the back of a lineout leading to a head clash between the two forwards.

Dalzell was the second man in the contact after Sam Whitelock took Hooper around the waist, who was falling to the ground as the Crusaders reserve lock went to wrap.

The Leichhardt Oval crowd was up in arms immediately over the hit, with boos clearly ringing around the ground. On replay, Stan Sport's commentator could only claim 'Wow' about the 'dipless' tackle after Dalzell had got away with a similar attempt moments earlier on flyhalf Tane Edmed.

By leading with the head, both players were sent reeling by the tackle which head coach Scott Robertson labelled as 'technically poor' although he reiterated there was no malice in it.

The red card came in 67th minute with the Crusaders back in the game at 17-14, and the loss of Dalzell was felt moments later as the Waratahs mauled over for a penalty try. Compounding matters, blindside Pablo Matera was sent from the field for collapsing the maul.

Head coach Scott Robertson said there was no doubt that Dalzell had to work on his tackle technique, but that every incident is different and it is hard to judge every tackle.

"It's hard to know. The second one was red. You look at it, it's such an interesting and difficult one to judge on," he said.

"Every one is so different. There is no sort of clear line.

"So look, obviously Dalzy's [Hamish Dalzell] tackle technique needs to get better, I know that. He's a big man and could have done better around it.

"It's a bit disappointing for Hoops [Michael Hooper] to take that head knock. There was no malice in it but it was definitely technically poor."