Cases from Monell to Praprotnik raised significant obstacles to successful § 1983 suits against cities.  To avoid those obstacles, plaintiffs increasingly framed their cases to argue that cities should be held responsible because they had failed to adequately train their employees.  While Tuttle had held that an employee’s constitutional violation would not—by itself—be enough to prove inadequate training, it left open the question of what evidence would be enough and what standard the courts should apply to inadequate training cases.

In City of Canton, the Supreme Court answered that question. It adopted a strict "deliberate indifference" standard under which plaintiffs were required to prove that the need for additional training was obvious and that the risk of Constitutional violations from the lack of training was severe.  The Court stressed that, in addition to deliberate indifference, the plaintiff needed to prove that adequate training would have prevented the constitutional wrong.   Finally, an influential concurring opinion by Justice O'Connor suggested that a plaintiff would have to prove that the city had failed to train the employee about either "a clear constitutional duty implicated in recurrent situations that a particular employee is certain to face," or a constitutional duty that the city knew had already been repeatedly violated by its employees.