A Though you pose this as a hypothetical scenario, it is not an implausible one. I encountered this situation following a group of pupils on an inspection a couple of years ago. They were reasonably well-behaved with most teachers but when they got to a maths lesson with a recently-appointed black African teacher with a heavy overseas accent, they behaved appallingly - making monkey noises to mock the teacher. In this lesson, the pupils never fully settled and they learnt very little.
Inspectors should not be altering their judgements about the effectiveness of a lesson according to the colour or sexual orientation of the teacher.
If pupils aren't learning anything, then the lesson will be inadequate whether the teacher is black, white, straight, gay or whatever. That does not necessarily mean, however, that the teacher is "blamed". In this case, the school had well-established "on-call" systems for teachers to ask for senior management team support with behaviour problems. Inspectors had seen them work effectively in other situations. In this lesson, the teacher hadn't used them.
In feedback, I was keen to find out why. There might, for example, be management and communication issues if new staff weren't all aware of the school's systems and procedures. In this case, it turned out that the teacher was aware of the systems but hadn't called on them out of a misguided sense of personal pride.
The significant points that were followed up in the inspection as a result of the observation were about the need for school leaders to reassure staff that the "on-call" system was there to support and help them and that there was no shame in making use of it. There were also points about racism - about which the school had been overconfident in assuring itself that it was being tackled effectively.
Both these points were rather more important than the judgement made about the teaching but, yes, that was unsatisfactory because the teacher had not coped with the pupils' poor behaviour and had not called on the support that was available to him. I would not, however, describe that as "blaming"
the teacher for the pupils' bad behaviour
Selwyn Ward draws on years of inspection experience. The views expressed here are his own. To ask him a question contact him at firstname.lastname@example.org