Dr. Not Yet Dr. Ag said:
Anyone able to explain what the significance of the Hawkeye to Ronin transformation is?
Ronin is ultimately sort of a more badass, no holds barred version of Hawkeye. He uses swords instead of bows. I think it's safe to assume that Hawkeye's family is dusted, which is what fuels the transformation. Pretty much a broken Hawkeye with nothing to lose.
Also in that scene they seem to be in Japan. The term "Ronin" stems from feudal Japan.
Here's what Ronin looks like in the comics (per Wikipedia)