When I was a child I was "taken captive by the Gentiles" [in the halachic sense] and enjoyed watching tennis. When I turned 16 I found out that one is not allowed to see someone wearing shorts if that someone is of the gender that singlehandedly populates the world [not that Martina Navratilova was anything to look at...] . So I stopped watching tennis - at least the female sort. Then I got a life and stopped watching male tennis as well. [Sorry "Mr. McEnroe"].
Now I am older and realize something else. A Jew should never be in a place where people won't be dressed properly. Anywhere. So if he HAS to go to work and not everybody on the train is dressed like a Beis Yaakov girl then he should keep his eyes down [in a sefer] and be busy with damage control. But if he is not compelled to go to a place then he shouldn't go there. Just because there is a heter for parnassa doesn't mean that there is ALWAYS a heter. Notice how many of the al cheyt's relate to Shmiras Habris Vi-haeinayim.
For example a Knicks game. There is no issur in seeing the players dressed in their fancy underwear [called "uniforms"] but if the women attending won't be dressed properly then one should avoid the game. Not to mention the problematic atmosphere of thousands of people going nuts over a silly ball as if it matters.
ובמושב לצים לא ישב - ועי' עבודה זרה י"ח