The incident occurred during a 10-and-under game between the Case Eagles and Milwaukee Colts in Mount Pleasant, Racine County.
The woman who captured the video, Caitlin Ocampo, told Storyful the Eagles were up around 20-0 against the Colts when a young Eagles player making a run was kicked by a Colts parent who had entered the field.
Eagles parents "were very upset and demanded he be ejected from the game," Ocampo said.
The Mount Pleasant Police Department said it responded to the scene after receiving a report that a man had kicked a child. Both parties had left before officers arrived but the suspect's "vehicle was stopped a short distance later," they said.
"The suspect was cooperative, admitted to the act, and acknowledged he was wrong. He was subsequently issued a citation for disorderly conduct. He was released without further incident," police said.
Officers also followed up with the 9-year-old and determined that he "was not injured during the incident," they added.
Eagles coach Channing Schultz, who was away for a family wedding at the time of the game, told local media that he was "filled with anger" after receiving calls about the "disgusting" incident. "It was the most cowardly act I've ever seen," he said.
"I have seen adults fight, I have seen fights at youth events, I have seen stuff happen, but I have never in my life seen a grown man come on the field," said Schultz, according to ABC affiliate WISN 12 News.
ABC7 Chicago contributed to this report.