I was having a dinner conversation with a far more literate person than I last night, she was saying how humans are the only animals that play games. I pursued this argument with much fervour. It is true that humans are the only ones that actually write out the rules of games - but humans are the only animals that can write.
Perhaps humans have more complex games based on strategy and deception, in games such as poker. Animals use deception in nature all of the time, with devices such as camoflage. It is true that this has an evolutionary purpose, but it shows how deception is rife within nature.
Anyone who has dogs soon realises, once you teach the game of 'fetch' to your animal - it is hard to get them to want to stop. Dolphins seem to spend most of their time playing below the waves. All animals seem to have a need to play, even if the animals are unaware consciously of the games that they are playing. Horses would not jump large obstacles unless they wanted to. Once an animal is aware of the game he is more than willing to play and learn.
So I propose that if animals could understand - then they would be filling up the stadiums also. Our enjoyment of sports is related to our love of play and perhaps that is something instinctive. It must be as sports have been around since man has been around, in every culture and every walk of life.