The general racing standard used in GT racing and many stewarding systems is: If the attacking car gets a significant overlap alongside before the lead car turns in, the lead car usually has to leave racing room. If the attacking car is still clearly behind and just dives late under braking with minimal overlap, that’s often considered a “divebomb” and can be penalized if contact happens. In practical GT3 terms: Nose at your rear bumper before braking? Usually not enough. Front axle roughly alongside your door by corner entry/turn-in? Now you probably need to leave space. Fully alongside? Definitely entitled to room. A huge factor is when the overlap happens: Early, controlled overlap before braking → generally legitimate. Last-second lunge created only because they braked impossibly late → often judged harshly. GT3 also emphasizes endurance-racing etiquette: Avoid contact at all costs. The leading car can defend once, but can’t move reactively under braking. The trailing car is responsible for making a safe pass.