A question – Off topic

This is a car accident/personal injury question. I’m sure some of you are well-versed in that area of the law. This is the setup: Two on ramps merge into one, leading to an interstate highway. One of those on-ramps has a yield sign. Assume that there are three cars going toward the highway on the non-yield side and one on the yield side.

The car on the yield side does not yield to the first car, which manages to pass it. The second car also manages to pass the car on the yield side, but the yield car is still moving forward. The third car on the non-yield side, which was following normal rules of traffic, keeps driving, because it has the right of way. Unfortunately, it is now to the side of, or slightly behind, the offending car from the yield side. They collide.

Is it a defense to any lawsuit that despite having the right of way, the third car is at fault (or at enough fault) that it should have followed normal rules of traffic and allowed the offending car to pass. Does the answer change if the third car hits the offending car from behind?

Ideally, following rules of traffic, the offending car from the yield side should have waited till all three cars had passed.