BRIAN Lake let himself and his Hawthorn teammates down with his undisciplined play in the third quarter of the Hawks' loss to North Melbourne on Friday night, coach Alastair Clarkson says.

"He was a bit scratchy tonight and we're pretty disappointed with that five or six-minute patch (in the third quarter)," Clarkson said after the Hawks' 20-point loss at Etihad Stadium.

"He let himself down and he let his teammates down and the game was right in the balance at that time. 

"He's been pretty good for us (but) he was pretty average tonight and we're disappointed with that. 

"But we move on and we hope that he responds from that."

Lake comprehensively lost his battle against North spearhead Drew Petrie, conceding five goals in two-and-a-half quarters before Clarkson moved Ryan Schoenmakers on to the big Roo. 

But it was a brain fade by Lake at the 11-minute mark of the third term that most disappointed Clarkson.

With the Roos two points down, Petrie marked a Levi Greenwood pass on the lead, when Lake decided a split-second later to knock the ball out of Petrie's hands.

The umpire then awarded a 50m penalty that allowed Petrie to convert from point-blank range.

It was Petrie's second goal in the space of three minutes and Lake's frustration shortly after led to an incident that is likely to be scrutinised by the Match Review Panel. 

After Lake tackled Petrie on the wing, the pair scuffled, the Hawthorn defender having his hands firmly on Petrie's throat as Petrie retaliated to Lake's face. 

It would ultimately prove a turning point in the match, with the Roos focusing their energies on the scoreboard, as Hawthorn unravelled with a series of undisciplined free kicks. 

From the time of Lake's 50m penalty to Ryan Bastinac's goal at the 23-minute mark of the term, the Roos kicked six goals in 13 minutes – including another from Petrie after he took a pack mark on the goal line – that took them to a 35-point lead. 

To rub salt into the Hawks' loss, they lost Bradley Hill before the game to knee soreness and Brad Sewell early in the first term with a right hamstring strain.

Sewell did not play his first senior game this season until round 10 after pre-season hamstring problems and now faces more time on the sidelines after hitting form in recent weeks.

"I'm not sure the severity of it, albeit he did it badly enough to be subbed out at the five-minute mark of the game, so that just disrupted us a little bit," Clarkson said of Sewell's injury. 

Clarkson said Hill had not experienced any knee pain in the week leading up to Friday night's game, but after taking a shot for goal during the pre-game warm-up it "did not feel right".

"With him and Cyril (Rioli) going out of our side, it just upset our balance a little bit, but you have to roll with the punches," Clarkson said.

"We've been really good at being able to cover for blokes who have missed, but we were unable to do it tonight."