Fights like these were actually only supposed to take place between strangers. The wikipedia article seems to only exist in german, so here’s a rough translation, sorry if it doesn’t read well, I’m not very good at translations. Also, as you can see in the pictures, the man in the pit had some kind of club as a weapon, at least according to Talhoffer

Gerichtskämpfe waren nur zwischen Fremden erlaubt. Durch einen entsprechenden Schwur von sieben Männern aus der männlichen oder weiblichen Verwandtschaftslinie der Kläger/Beklagten sollten Kämpfe zwischen Personen bis zum fünften Verwandtschaftsgrad ausgeschlossen werden (https://de.wikipedia.org/wiki/Gerichtskampf_zwischen_Mann_und_Frau_(Hans_Talhoffer)#%3A%7E%3Atext=Gerichtsk%C3%A4mpfe+waren+nur+zwischen+Fremden+erlaubt)

Legal Court fights were only allowed between strangers. Through an oath of seven men from the male or female line of relatives of the accuser/accused, fights between persons up to the fifth degree of relationship were supposed to be prevented