What would be the equivalent activity today to the ancient romans watching gladiators fighting?
Any of the combat sports today can be compared to gladiatorial fights; such as boxing, bull fighting, and wrestling. Any sport or entertainment that pits man against man or man against beast is a candidate for that distinction in my opinion. The Ancient Romans also loved to watch chariot races which can be compared to car racing and horse racing of today. In fact, you could make endless comparisons between our modern society and that of Ancient Roman society.