David Calton, 19, was playing for Mount St Mary's Catholic College in North Derbyshire when he was involved in an altercation with Andrew Wilson, playing for the other team. Wilson, a pupil at Pocklington Grammar School, East Yorkshire, was knocked out and suffered a broken jaw.
Calton was sentenced to 12 months in a young offenders' institution at Sheffield Crown Court yesterday after he pleaded guilty to causing grievous bodily harm.
Judge Robert Moore said: "Any sportsman, boy or adult, amateur or professional, who deliberately injures another will face immediate custody to prevent others from doing the same."
The boy's father, Chris Calton, said: "I feel it's grossly unfair and I will do everything I can to get the sentence reduced. My son is not a criminal.
"Rugby is a physical sport and injuries do occur from time to time. David has suffered injuries in the past and got a broken nose in the game in question. I just can't understand how the British legal system can do this to a schoolboy."
Mr Calton, an engineer who lives in Hong Kong, said the court case had devastated his son. "The threat of legal action has been hanging over him ever since the match took place in January. We were led to believe it would never reach court and then when it did we were told he would be let off. We are all distraught."
He said the court case had affected his son's education and caused him to do worse than expected in his A-levels. He had hoped to read law but instead opted to study tourism and recreational management at Sheffield Hallam University after getting disappointing grades.
"He had only done two weeks at Sheffield but he had settled in well and his prospects were good. Now his life is in tatters. He's a big lad and on the surface he's been very brave but inside he's as nervous as hell.
"He's really only a little boy and I'm furious with what has happened to him."