Monks’ rules and their analysis
Monks’ Training (Sekhiya) 67
Head muffled up means: it is so called if he is dressed, including his head, in his upper robe.
Dhamma should not be taught to (someone) with his head muffled up (and) who is not ill. Whoever out of disrespect should teach dhamma to (someone) with his head muffled up (and) who is not ill, there is an offence of wrong-doing.
There is no offence if it is unintentional, if he is not thinking, if he does not know, if he is ill, if he shows the head having caused it to be uncovered, if he is mad, if he is the first wrong-doer.