Police used CS spray to separate brawling parents in front of children in the playground of a primary school.
Officers were forced to use pepper spray on a man believed to be assaulting a pupil's mum at Penryn Infant School in Cornwall.
As children waited to be collected, a dispute between two mums turned ugly when relatives of the two women began 'behaving in a disorderly way'.
One man was arrested and has been released on bail, pending further inquiries.
A spokesman for Devon and Cornwall Police said: "The use of CS spray is an effective tool for officers, particularly in public order and violent incidents, in order to prevent escalation of an incident, to bring it to a swift conclusion and prevent injury to victims and innocent members of the public."
Officers attended the school last Thursday following reports a fight between two mums in the playground earlier in the day.
They remained at the premises to prevent a 'breach of the peace', according to PC Jules Evans.
PC Evans told the West Briton: "The male involved would not heed advice and became very aggressive and assaulted another parent.
"As a result of his behaviour, we were forced to use the spray and physically restrain him."
Headteacher Gillian Wright told the paper she had written to parents about the incident.
She said: "Children who are very young have witnessed something they never should have. That behaviour should never have happened. Safety and happiness are the most important things for children at the school."
Mrs Wright said those involved in the incident had been banned from both the infant school and neighbouring junior school until the end of term in July.
Officers from Devon and Cornwall Police visited the school the following day to reassure students.