For the purposes of sentencing ABH offences fall into three categories, Category 1 being the most serious and category three the least. Regardless of your previous convictions or your plea, committing the matter to the Crown Court (either for trial or sentence) can only be a consideration if the offence falls into Category 2, and even then there must be a number of aggravating features. Category 1 offences should normally always be dealt with in the Crown Court whilst Category 3 offences should normally be dealt with in the Magistrates' Court.
From your description of events I would say that the offence falls into Category Three. You can see the factors that help categorise the offence on page 225 (that's p.225 of the PDF file, page 201 of the document itself) of this document:
http://sentencingcouncil.judiciary.gov.uk/docs/MCSG_Update9_October_2012.pdf
Even if the Magistrates' do decide the offence crosses into Category 2 there does not seem to be sufficient aggravating features to move the offence towards the upper end of the sentencing range.
Your previous of course does not help your cause and you should discuss the full facts with your solicitor. You will lose the right to any discount if you plead not guilty but are found guilty at trial. Your brief may be able to negotiate with the prosecution if you should agree to a guilty plea to a lesser offence of Common Assault.