Circus

Question

I just noticed some recent posts about the circus and baseball games, etc. I admit that I must look in to this further, but just on first thought, weren't those prohibited because they were promoting avodah zarah and ideas which were contrary to yahadus? I am not saying there are any great ideas being promoted at baseball games, but that seems more of an idea of stupidity than actual falsehood. I am not saying people should spend their time at baseball games or concerts, there are certainly more productive things to do with one's time. But as far as an issur is concerned, it seems there is a difference. But admittedly, I need to research this further. If you know offhand, could you tell me where that gemara is. I can track it down, but you could save me time. I will try to review it over Yom Tov -- during chatzi lashem.