I would like to understand the logic (if there is any) behind the phrase "best-of-x" (where x is a number) in the context of competitions, most notably sports. I understand that best-of-five implies that the party that first wins three games wins overall. However, why is the preposition of used? Why not "best in three (games)" or "best over three (games)"?
"Of" expresses the relationship between a part and a whole
"In" expresses the situation of something that is or appears to be enclosed or surrounded by something else
"Over - extending directly upward from, at a higher level or layer than
it refers to parts of the whole.
You would say "They have won three of five games". You would not say "They have won three in five games" or "They have won three over five games"