Both religion and football require obedience to particular rules, codes of conduct that must not be broken. Whether it's the Ten Commandments or the requirement to hate Celtic if you're a Rangers fan. Football does dominate the lives of many. But I don't think having dedicated fans is enough to class football as a religion. There is no belief in a super-human controlling power in football.
Fans watch, support and maybe even worship eleven men running around a pitch every weekend.
That doesn't seem very spiritual. Gods are worshipped by their devoted followers irrespective of their current track record. The faithful don't get angry if God doesn't deliver a miracle every week. Football fans on the other hand do get very annoyed if their teams are not performing to the expected level, and miracles are often demanded. While traditional religion is becoming less and less popular in many parts of the world it is not really likely that football is to blame for this trend.