In China, depictions show horse riders using sticks – an ancient sport perhaps reminiscent of modern-day polo.
Similar, curved sticks have been unearthed in Yonghai but the researchers have found no direct connection to the balls.
Dating efforts suggest the sticks belong to a more recent period than the balls.
Dr Wertmann said: “Therefore, the leather balls from Yanghai are not connected to early forms of field hockey or polo, even though two of the balls were found in the graves of horsemen.”
What is likely, however, is the balls were played in a team-based goal sport.