BUENOS AIRES — Arsenal must score five goals more than the visiting Italian powerhouse A.C. Milan on Tuesday to advance to the quarterfinals of the Champions League, Europe’s most prestigious soccer tournament. Though such a comeback has happened only three times in the tournament’s 57-year history, some know better than to rule it out.

“It all depends on if Arsenal fans are up for it,” said Michael Dennis, a soccer fan from Yorkshire, England, who is a founder of the Web site Fan Chants. “The team could walk out and get immediately buzzed off the crowd and start firing.”

Fan Chants is a repository of more than 20,000 chants for more than 700 teams worldwide. From nasty to boring and folkloric to funny, the chants are a window into how a team’s fans fire up a stadium: Italian chants are melodic, Greek chants are foot-stomping, English chants are creative.

“The reason people love football is not just the actual game, but the buzz and the sounds of being there,” Dennis said.