This question was previously migrated from Law, but then rejected and returned on the grounds that it was already answered on Wikipedia. But this essential aspect of the question is not addressed on Wikipedia, and it is perhaps what I was most interested in. What types of weapons or protective gear would have been permitted, if any?
And would the battleground have been enclosed by a wall or a cage or similar?
I've taken the liberty to expand on the original post. This case is so well known in legal circles, being mandatory in first year law under every English Common Law Jurisdiction including the U.S.A., I think OP can be excused for thinking it might be universally recognized here also.
"Ashford v. Thornton" was an 1818 English legal case standing for the principle that all law remains until it is repealed.
In 1817, Abraham Thornton was charged with the murder of Mary Ashford, but the jury acquitted the defendant.
Mary’s brother, William Ashford, launched an appeal at the King’s Bench. The defendant claimed the right to trial by combat, a medieval usage which had not been specifically repealed by Parliament. The prosecution stated that a law ought to become invalid if it was not used for centuries.
The court decided that all law remains until it is repealed; therefore, Thornton was granted trial by battle. Ashford declined the offer and Thornton won his case.
After this ruling, Parliament, the next year, repealed the right to trial by combat.
Links for Ashford v Thornton (1818):