The type and complexity of the assessment approach will vary with the reason for assessment, previous levels attained by the student and the type of outcome to be assessed. A role in a drama performance or dance, music and physical education would certainly fit this area. Group work poses a real problem. The possibility of someone either not contributing effectively puts at risk valid assessments, either for an individual or a group. Sometimes peer assessment is a suitable way to resolve the issue.
Teachers make professional judgements all the time.
But the key word is 'judgement' - that is to say, the statement or assertion from the teacher is based on a judicious process. A professional judgement is generally regarded as a formal decision involving formal processes, based on agreements and standards and involving discussion with others and reflection on evidence gathered. It must be validated with others and reflection on evidence gathered. Judgements made on verified evidence are more likely to be consistent and teachers will be more confident in making them. To achieve consistency teachers need to develop a shared understanding within and across schools about standards and assessment of standards.