Rosberg was to blame for US GP clash

Let's not pull any punches: to win a Formula 1 drivers' world championship you must have that killer instinct. The true champions certainly don't hold back.

There are 19 other drivers out there, and to be top of the pile you need to score more points than any of them. And sometimes, to do that, drivers need to get their hands dirty.

As we have seen over the years, when a team puts together a line-up with two number-one drivers there will be fireworks.

Just look back to Nigel Mansell and Nelson Piquet at Williams, Alain Prost and Ayrton Senna at McLaren, Sebastian Vettel and Mark Webber at Red Bull to name but a few. Now we have Nico Rosberg and Lewis Hamilton.

If a team is organised in a way with a clear number one and number two, as at Ferrari during the Michael Schumacher era, it eliminates the risks inherent with two lead drivers.

But does this make Schumacher a less worthy world champion because he was always racing against a team-mate who wasn't allowed to beat him? After all, it eliminated one of his leading rivals, particularly in the years where Ferrari produced by far the best car.

Team-mates don't have to share a double room, they don't have to drink and eat together, but they must always work collectively and for the good of the team. That means putting the maximum effort into pushing the team forward.

Mansell won five races for a dominant Williams in 1986 and Piquet four, but Alain Prost won the drivers' title for McLaren © LAT

They must respect each other on the track, but when it comes to the drivers' title it's all about outscoring the other 19 drivers. The key is being viewed by the team as the man that will get the job done, so it's essential you're better than your team-mate, both in terms of speed and race results.

Let's take the Hamilton v Rosberg incident that is most recent in our minds - the one at the first corner in Austin on Sunday.

If you had to ascribe blame, you would have to say that it was Rosberg's fault. Why? Because he was on pole position and he made a bad start, as he has done quite often.

That allowed Hamilton to get alongside him into Turn 1 and then hold his place on the inside line. That is what racing is all about.

Was Hamilton a bit heavy handed on the exit of the corner? He probably was. But if he had been racing Sebastian Vettel or Daniel Ricciardo, we would have simply said 'this Lewis Hamilton chap is a real racer'.

But because he did it to his team-mate, everyone starts asking questions and pointing fingers.

Mercedes keeps telling us that there are no team orders. By the time the United States Grand Prix started, the constructors' championship was well and truly won. So if what the team says is true, then Rosberg would have been perfectly within his rights to keep his car on the track at the exit of Turn 1.

Now, two things could happen if you do that. First, you could argue that there would be contact and you might end up with one Mercedes on its rollhoop in the runoff area.

Hamilton's ruthlessness has been seen before, most recently at Suzuka © XPB

Maybe, but I think the second possibility is more likely. That option is that Hamilton would simply have tightened his line and both would have survived.

If you look back to the Japanese Grand Prix a couple of races ago, a very similar thing happened. Rosberg was pushed wide on the exit of the second corner by Hamilton and he lost four or five places.

Immediately, his race was transformed from one of going for victory to a simple case of recovery.

You would think he would have learned from that. But no, again he tried to fight Hamilton to hold on to the lead, and in doing so he lost momentum and positions.

While he continues to make that kind of decision, he is always going to lose out to Hamilton in battle, and it's clear there is something in his head that is stopping him making the right choices.

I think this all goes back to the Belgian Grand Prix in 2014 when he and Hamilton really did come together and cost Mercedes a race victory.

We in the press made such a big deal of it at the time, meaning the team had to address the situation.

Whatever Mercedes' chiefs did or said to Rosberg and Hamilton behind closed doors is still ringing loud in Rosberg's ears. And you can be absolutely sure Hamilton knows that very well.

Webber rarely had an answer for Vettel during their time as Red Bull team-mates © XPB

Even more importantly, Hamilton knows that because of this Rosberg will give him room. So he, quite rightly, pushes it to the limit again and again. That is why he is a three-time world champion and Rosberg hasn't won one.

It's the same as Sebastian Vettel being a four-time champion and longtime team-mate Mark Webber not having won it.

In both cases, they are drivers capable of being just as good as their illustrious team-mates. But it comes down to not quite being cut-throat enough about it to get the job done.

As Webber said on the radio after winning the British Grand Prix in 2010, "not bad for a number two driver". He was right, and I'm afraid to say that this is the kind of thing we might expect to hear from Rosberg soon.

You can draw further comparisons between Rosberg and Webber. The Australian came close in his first year as a title contender, but wasn't able to thereafter. It might be that Rosberg's best chance to be champion was in 2014, and he is now cast as Hamilton's support act even if he does have joint number one status.

The question now is how he responds. As a team - which, remember, is made up of dozens of people at the track and hundreds at the factory - you never want to see hard work go to waste when two drivers collide.

I've had drivers do that in the past and it's not much fun - you have to knock some heads together afterwards to sort it out.

But in Rosberg's position, he needs to find some of that edge, that killer instinct, which all the great champions have in some manner.

The question is whether he has it in him.