There’s a fine line between defending your position and blocking, and unfortunately, it’s become even finer in modern times. In efforts to remove any chance of a collision, the governing bodies have established, generally speaking, a few fine rules about appropriate behavior with a driver in one’s mirrors. Movement in reaction to an opponent and “driving your mirrors” is a big no-no, since two cars squeezing one another and jousting aggressively on the way into the corner is a great way to tangle wheels with open wheel cars.
Instead, a defending driver is given one move on entry, and that one move has to be preemptive and cannot respond to an attacker’s move with any great vigor. However, there is a certain gray area when it comes to defending and what tricks one can use to keep an opponent behind.

When fighting for position, the best always give one another the slightest amount of room to function within.
One way to protect one’s space is widening their car. In order to make a car “wide,” a driver will drive just a few feet off-line, where there’s still plenty of grip and cornering speed isn’t compromised too much. This prevents an attacking driver from passing by minimizing the area in where an overtaking maneuver could take place.
Squeezing another driver is a trick used more commonly across the pond, where rules a a little more relaxed. By pushing a driver out towards the edge of the track, one can intimidate a faster competitor into lifting or momentarily hesitating. It becomes quite dangerous very quickly though, so it’s really not condoned in many American series. Predictably then, it’s seen as contentious and some drivers abhor the move, whereas other feel it’s their right to defend their real estate in whatever way they choose.
However, one of the best means of defense has less to do with car placement and more to do with focus. By relying too much on one’s mirrors, some speed is always lost. For the ability to cover ground quickly and effectively, it pays to pay no mind to the driver behind. In other words, a good defense is a great offense. Focusing on one’s own performance and less about the others will keep one from worrying and allow them to focus on the issues in front of them, which will often keep them ahead. There’s a balancing act going on here.
While these sorts of rules are well-intended, they sometimes spoil the spectacle. In the name of absolute safety, the dogfight has been neutered somewhat. Now drivers fear for the eligibility of a pass prior to making it, and some of that shoot-from-the-hip fireworks have been lost. With modern passing rules, this brilliant dummy on Nelson Piquet from Nigel Mansell would not be legal:
Ultimately, drivers need to give one another a bit of space, room, and respect when dicing. Only amateurs and unscrupulous drivers will chop people too aggressively and put their own race in jeopardy. Of course, incidents will always happen, but between two greats (see above), a little bobbing and weaving can be pulled off without endangering either party, and the spectacle is all the better for it.