In Italy according to the National Sport Federation (CONI) there are 4,7 million members officially registered with a National Sport Federation. Football with 1,05 million (22% of total) is the largest sport federation. Here the top 10:
Football: 1,05 million / Tennis 560K / Volleyball 410K / Basketball 290K / Athetics 270K / Swimming 160K / Sailing 150K / Gymnastic 120K / Martial Arts 110K / Winter Sports 100K