Google has a neat application which lets you track interest in a topic according to how much attention it receives. The chart at the top of this page shows for 2004-2013 the results of a Google Trends search on
You can clearly see the seasonal cycle of interest peaking during the seasons and falling off during the offseason. The data show that soccer remains in fourth place of the five sports, with only hockey trailing. The exception is during the 2006 World Cup when soccer rivalled basketball for 2nd place in peak interest. Interestingly, soccer shows no signs of increasing interest, but football and basketball do.