In the U.S., anyone can file a lawsuit against anyone else for any reason, or for no reason at all, with virtually no risk. A plaintiff on his own or with a lawyer on a contingency fee can roll the dice with the legal system and maybe get a jackpot verdict. At the very least he can force a company to spend time and money getting the case thrown out. The law has made a little progress in containing the worst misuses of the courts. Like the convict who sued his prison cafeteria for serving him a broken cookie.
Prisoners are a major source of lawsuits and appeals.
They have plenty of time on their hands and easy access to law libraries. Casinos stuck with bad markers can file lawsuits in courts. The first step is checking to see if the plaintiff has made any procedural mistakes. Defense attorneys look for these first, because if they do not object immediately, they may have accidentally waived away their defense. A common mistake made by non-lawyers is filing suit against entities that do not actually exist.