It is revealed in "Avengers Endgame," that during the five years after Thanos killed half of all life, Hawkeye (Jeremy Renner) took on a new mantle, Ronin, and went on a rampage on the criminal underworld.
It is explained that he was killing criminals because they got to live when good people like his family died in the snap. Whilst Hawkeye seems to have put his dark days as the Ronin behind him, it is likely he had angered a lot of criminals and their families during his rampage.
The trailers for "Hawkeye" show a new character, Kate Bishop (Hailee Steinfeld), wearing the Ronin suit, which could bring all sorts of criminals after her to get revenge on Hawkeye.