DISTURBING video has emerged of a teacher, who was later sacked, being repeatedly punched in the head by a former school student.

But the Education Department deemed Adelaide's Reynella East College teacher Michael Eglinton's behaviour towards the youth was "disgraceful and/or improper" because he protested as he fended off punches with his open hands, exclaiming: "You're mad" and "You're crazy, boy".

The teacher deflects some of the punches thrown by the 17-year-old.

Last month, the South Australian Teacher's Appeal Board ordered Mr Eglinton be allowed to return to work, but a video of the incident has now highlighted the extraordinary reaction by the department, which was criticised by the board.

The video, taken at a bus stop outside the college by another student at the preschool-to-Year 12 campus, begins when a youth who had been expelled from the school runs towards Mr Eglinton and aims multiple blows at his head.

Mr Eglinton deflects some of the punches while exclaiming to the 17-year-old attacker, who cannot be named, "You're mad" and "You're crazy, boy".

He was sacked by the department for being "disrespectful".

Read more at the Adelaide Advertiser