Mercedes technical director Mike Elliott has revealed Valtteri Bottas thought he was going to have more grip than he actually had at the start of the Hungarian Grand Prix which is why he dropped down the order immediately.
Bottas started from second place but fell behind several cars including Max Verstappen, Lando Norris and Sergio Perez. He then caused havoc when he outbraked himself at Turn 1 to heavily damage three of his rivals cars.
"I think you need to bear in mind that the conditions were really tricky for the drivers," said Elliott on Mercedes' post-race debrief video. "When we formed the grid up, got everything ready it was raining quite hard.
"But that rain dropped off and by the time we set off for the formation lap, actually it was pretty dry and Valtteri felt that he had quite a bit of grip. They obviously go around their lap and as they go around that lap, the rain started to really pour down and when they formed up on the grid for the proper start, there was a totally different grip level available.
"The drivers have been practising all week for that start, that start in the dry, and they got down a pattern of where they want to be with their clutch and so as we went for that start, the driver has got to pick where they think they are going to put their clutch, how much grip do they think that they have got and it is really a guess.
"In Valtteri's case he thought he was going to have more grip than he actually had and as a result of that, he got a lot of wheelspin and that wheelspin just means that you have less grip from the tyres and you get away much more poorly and that's why he had a poor start.”
Bottas hit the rear of Norris as he misjudged his braking point, causing the McLaren driver to crash into Verstappen. The Finn also collected Perez in a secondary collision and has been given a five grid-place penalty for the Belgian Grand Prix for his actions. Elliott says Bottas felt very guilty about the incident.
“Valtteri obviously had his poor start, he had cars coming round him from either side and he was sort of squeezed going into that first corner," explained Elliott.
"The drivers are trying to work out where their braking points are and they are doing that not really knowing exactly how much grip they've got, how much is the rain going to affect their grip, when should they brake, when will the cars around them brake.
"And Valtteri picked his braking point and unfortunately he braked slightly too late and in doing so he locked up his front tyres and as soon as you have locked your wheels, you have lost grip and he just slid into the car in front.
"I know speaking to Valtteri afterwards, he felt really guilty for what had happened, really sorry for his competitors he had knocked off and he was apologetic to both the team and also his fellow competitors. That's obviously not what he wanted to happen.”