Willenhall school pupils threw food at Ofsted inspectors
Students pelted school inspectors with food and jostled them in corridors during an Ofsted visit, according to the watchdog's report.
It found sixth formers at Willenhall E-ACT Academy in the West Midlands were afraid to leave their common room because of younger pupils' behaviour.
Inspectors rated the school inadequate overall, noting that "during 2015 and 2016, 70% of teachers left".
The BBC has contacted school sponsor E-ACT for comment.
In a letter sent to parents following the critical report's publication, E-ACT said it had "strong leadership" in place "driving standards" and was "confident that Willenhall Academy will continue to make rapid progress".
The school - which Ofsted described as "coasting" - was inspected in March and almost a third of pupils were found to be regularly absent.
Individual aspects of provision were also given a rating of "inadequate" - among them the quality of teaching, which was described in the report as "weak", and pupil behaviour.
"Persistently poor behaviour at social times and in lessons leads to many pupils feeling unsafe and not learning well," the report said.
A third of the staff who responded to an online questionnaire said they did not feel pupils were safe.
Oftsed said E-ACT "fully recognised the challenges" and had begun to "address aspects of greatest concern", with its leaders' judgements "fully in line with inspectors' experiences and evidence".
However, it said leaders and sponsors had overseen a decline in standards since a previous inspection in 2015.
"While there is an ambition to address inadequacies and to raise aspirations, there is not yet a sustainable track record in the school to suggest capacity for improvement," it continued.
E-ACT's letter to parents said it was "proud of the fact that almost two thirds of our academies are rated at least good".