Formula 1 outlaws moving under braking after protests over Max Verstappen
Drivers' concerns about the defensive tactics of Red Bull's Max Verstappen have led to Formula 1 outlawing moving under braking.
The Dutchman has employed this tactic as a trademark in battles with rivals but many other drivers have complained that it is extremely dangerous.
Race director Charlie Whiting was told at the US Grand Prix that there would be a big accident if he did not act.
Whiting has issued a ruling saying such moves will be considered illegal.
"It is like it is," Verstappen said about the rule.
"It's good to make it clearer what's allowed and what's not.
"I'm just going to race and then we will see how it is going to be defending and how it will affect the racing."
This is likely to become known as the "Verstappen rule" after a series of controversies involving the 19-year-old this year.
These have included his battles with Ferrari driver Kimi Raikkonen at the Hungarian and Belgian Grands Prix, and with Mercedes' Lewis Hamilton at the last race in Japan.
Mercedes lodged a protest against Verstappen's driving in Suzuka, which resulted in Hamilton taking avoiding action and going up the escape road at the chicane, but subsequently withdrew it.
The drivers' concerns about Verstappen's driving focus on two main areas: moving - or changing line - under braking; and what is called "wait-and-move".
The second is when a driver defending his position waits to see which side the driver behind will attack on and only moves to defend after he has done so.
Many drivers consider both situations to be dangerous and even dirty because they are already on the limit during braking so cannot brake harder and avoiding the car in front is difficult.
Whiting has been confronted about the issue a number of times this season. His initial response was that Verstappen was driving on the edge but just within the bounds of acceptability.
Verstappen has twice in recent races been taken aside by Whiting and warned to be careful about how he drives in such situations.
But after repeated complaints from the drivers, Whiting has been persuaded that he needs to take action.
His new ruling is predicated on article 27.5 of the sporting regulations which states that "no car may be driven… in a manner which could be potentially dangerous to other drivers…" and article 27.8, which prohibits any manoeuvre "liable to hinder other drivers, such as… any abnormal change of direction".
The drivers and teams have been reminded of article 27.6, which says: "More than one change of direction to defend a position is not permitted. Any driver moving back towards the racing line, having earlier defended his position off-line, should leave at least one car width between his own car and the edge of the track on the approach to the corner."
Four-time world champion Sebastian Vettel, a director of the Grand Prix Drivers' Association, said: "It is very simple. The day I joined F1 it was clear and it was a sort of unwritten law, and in recent times we have had situations and got away with it.
"So for sure then the message is that everyone is starting to do it. It is the wrong thing because, as we spoke about yesterday, we are just waiting for something to happen. Therefore I think it is a good action."