Mako Vunipola - Lions villain or a risk worth taking?

One of Warren Gatland's biggest decisions this week before what must rank as the most important test of his career is what to do about Mako Vunipola.

The 26-year-old, a son of Tonga international Fe'ao, was born in Wellington, raised in Wales and represents England, and is one of the most talented players among Gatland's front rowers.

Vunipola is one of those rare beasts as a prop currently operating in the Northern Hemisphere in that he can run, pass and step off either foot. He's powerful and quick too, and possesses a freakish ability to keep going for close to 80 minutes despite possessing a 121kg physique which might suggest otherwise.

He is a quality player but the problem is that he is also approaching loose cannon territory and, while reference to the Lions' discipline (or lack of) was made by assistant coach Graham Rowntree a day after the visitors' triumph, a failure to regain control of one of his heaviest pieces of artillery could be extremely costly for the Lions.

Vunipola's yellow card late at Westpac Stadium during the Lions 24-21 second-test win could easily have been a red. It was shown for what is euphemistically called a "ruck cleanout", but which in reality was an act of thuggery; Vunipola leaving his feet to dive, shoulder first, at a prone and defenceless Beauden Barrett, a contact which came perilously close to the No10's head.

Minutes earlier he shoulder-charged Barrett after the All Blacks playmaker's clearing kick. Referee Jerome Garces had little choice but to reach for his pocket; it was just a matter of the card colour.

A week earlier, Vunipola hit Anton Lienert-Brown in what he may have thought was a ruck cleanout - had the ruck still been formed - but was in fact a late swinging arm on an opposition player who had turned his back and was watching the ball being delivered to his backline.

Vunipola later admitted that in the same test he grabbed All Blacks prop Owen Franks by the testicles in a scrum. His bind had slipped, explained the Lions loosehead, and he had to reach out for something or risk being penalised for collapsing the set piece.

One can only assume Gatland is aware of the constant treading of a very fine line by Vunipola, and while forwards coach Rowntree refused to single anyone out in Wellington on Sunday, it was as if he was in fact targeting someone in particular.

"It's not as if it's the same individuals," Rowntree said. "There's a trait to what we're doing. We just can't be doing it. We can't lose a test series on the back of some stupid penalties. That would be unacceptable. How would you live with that for the rest of your life?"

The All Blacks will be acutely aware of Vunipola's growing list of transgressions, and while coach Steve Hansen has refused to make capital out of them - unlike Gatland who explained he just wanted to protect his players when complaining about the treatment of halfback Conor Murray in the first test - it must grate that the Lions player has escaped them all with just a single yellow card.

Will Gatland warn Vunipola and select him anyway, or will he consider him too much of a red flag and drop him to the bench? The Kiwi coach has shown his liking for taking chances on this tour, so the former will probably apply. But the risks are real.