Step 1: Picture the situation.
Two or more persons fight in a public place and disturb the peace of that place.
Step 2: Eliminate the other public order offences.
Riot needs an unlawful assembly of five or more persons with a common object, abetment means instigating someone else's offence, and conspiracy needs an agreement to commit an illegal act, none of these match a simple public fight between two persons.
Step 3: Identify the exact offence.
Section 159 of the IPC labels this specific situation, a fight between two or more persons in a public place disturbing public peace, as Affray.
\[ \boxed{\text{Affray}} \]