Get them to try and drop the intent (might get a plea bargain on that one). That he didnt mean to cause such injury, he was upset, distressed and worked up at how this person had abused him.
If there was no way he can prove that he acted in self defence then I suggest he pleads Guilty at the FIRST OPPORTUNITY to reduce 'any' sentence, Community or Custodial that he might get.
Get a GOOD Solicitor or Barrister who can mitigate his circumstances with DRAMA
Ask for committal to Crown Court (Judges appear to be more lenient than Magistrates, because they see a lot of horrible things and a first time offender may get him a lighter sentence in the Crown Court.
If your friend drinks, get him to go for alcohol counselling (even if he doesnt need it) to show he is doing something
Get a list of Anger Mangement Programmes off the internet and get him to tell the Court and Probation Service that he is doing something with his anger (i.e. not forced)
When he goes for his pre sentence report, show ABSOLUTE, PITIFUL REMORSE, write it all down on pages and pages and pages of how Sorry he is, that he didnt know what came over him.
Get on with the probation officer.
Make sure he has a full time job AND DISPOSABLE income, a mortgage to pay, responsibilities etc.
Say he was privately educated with a plethora of qualifications.
This was OUT OF CHARACTER.
On this note, the Judge prior to asking for a PSR will tell him (but they tell everyone this) that he may be likely for a custodial sentence.
If he does ALL OF THE ABOVE, and IT REALLY IS a first offence, he may also be able to provide character references in person or in writing at the Court - then he MAY BY THE SKIN OF HIS TEETH get 240 hours Community Service, The Think First Programme, and a Grands worth of fines AND Compensation to pay.