Experimental tasks depicting a bullying scene are being studied to elucidate the causes of bullying and to verify methods for resolving bullying. Bullying involves not only victims, bullies, reinforcers, who are complicit in the bullying, and defenders, who mediate the bullying, but also bystanders, who ignore the bullying. Bystanders comprise the largest group involved in bullying and can play an important role in resolving bullying. However, in previous experimental tasks depicting a bullying scene, participants could not perceive bystanders’ behavior as different from the behaviors of the victim or bully. The present study aimed to contribute to the development of solutions to bullying by creating experimental tasks, including a measurable behavior representing bystanders. In this research, we introduced a new option of behavior representing bystanders in a “catch-ball task” that can express the reinforcing and defending behavior in a bullying scene. Results of our questionnaire survey showed that the newly implemented behavior representing bystanders was perceived as bystander’s behavior by participants. Moreover, according to the results of another questionnaire survey, the improved experimental tasks with one bystander were perceived to be closer to a bullying scene compared with previous catch-ball tasks.