It is very dangerous when you push someone off the track as they are trying to overtake you at that speed - especially at Monza. You are doing more than 180mph through the Curva Grande in a Formula 1 car.
The problem was that Vettel moved towards the other driver in a very aggressive way - and at a very high speed - and he did not leave Alonso enough room to stay on the track.
Alonso was not behind; he was already past half of Vettel's car. If you do that, you have to be penalised.
I can tell you it's not nice to be on the grass at 180mph in an F1 car. The situation for Alonso was very difficult.
Vettel shows overtaking mettle at Monza in 2011
Once you are on the grass you lose a lot of grip and it's very bumpy. You need to back off to get your speed down and fight the car. The key is not to crash, which he managed to avoid doing.
It was not at all the same situation as last year, when Vettel passed Alonso in the same place with two wheels on the grass.
Then, Alonso left room for one car. On Sunday, Vettel did not.
“Alonso has a significant points advantage, so what McLaren and Red Bull need to do is be consistent and finish in front of him”
The thing I don't understand is how Sergio Perez and Sauber had such strong race pace.
I was quite surprised with his second stint when he was on the medium tyres and the front-runners were on the hard tyres.
I don't understand how he could continue to be as fast as he was - a second faster than anyone else - because I don't believe there is that much difference between the hard and medium tyres.
I also ask myself why Sauber have not done this in the past and had the same pace. It was quite surprising for me, and I'm sure for everyone else too.
You have to expect them to be able to do that again in another race, because otherwise it does not make any sense.
It was predictable that Red Bull would struggle at Monza.
They are never very good on top speed and this year they have been more badly affected than anyone else by the ban on exhaust-blown diffusers, so they do not have the downforce to make up for that lack of straight-line speed.
They are also having reliability problems and that was a significant blow for their championship hopes.
Alonso has a significant points advantage and is finishing virtually every race in the top three or five.
What McLaren and Red Bull need to do is be consistent and finish in front of him.
Jaime Alguersuari, BBC 5 live's F1 analyst, drove for Toro Rosso in F1 from 2009-11. He was talking to BBC Sport's Andrew Benson
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