in turn nine?

[goodsogi]

I am reading an article about car racing. I met this sentence.

"Button started in second behind Sebastian Vettel, but when Vettel went onto the grass in turn nine of the first lap, Button made his move."

I don't understand the blue part. Can you say it another easy way, please?

[2006]

I am reading an article about car racing. I met this sentence.

"Button started in second behind Sebastian Vettel, but when Vettel went onto the grass in turn nine of the first lap, Button made his move."

I don't understand the blue part. Can you say it another easy way, please?

I don't know if I can say it another way, but I can explain what it means.

The cars are on a winding racetrack that has at least nine turns. When Vettel's car went off the track and onto the grass at the ninth turn, Button had a chance to get ahead of Vettel and made his move to do so.