Do you think it is sinful to watch American Football games?

If all you're doing is watching the game, then no.

I actually started a thread a while back asking if it was sinful to watch games played by the Rams, because of their drafting of a sodomite.

I decided that I can watch games played by them.  I did because the rationality of not doing certain things which have some sins in them is universally impossible in the modern world.  If it is sinful to watch a football game where there are sins (cheerleaders, working on sunday, promotion of ɧoɱosɛҳųαƖity) then by that same logic it is almost impossible to do anything!  
Is it sinful to go to home depot? - they are a supporter of gαy rights.
Is it sinful to go to work where women are immodest according to Catholic modesty standards?  

Watching football does not facilitate or promote the sins involved.  If Catholics did not watch football the ratings might decrease from 5 million to 4.99 million. (as 99% of 'catholics' are not catholic.)
When watching obviously avoid looking at any cheerleaders, and protest publicly in any chance you have against the sins.


Also another thing that I don't think anyone has ever talked about before is....The immodesty of the (Male) players!!
Contrary to many Catholics thinking, there is immodesty for men!  The men wear ultra tight clothing - - Yes the clothing makes playing football much easier but it doesn't have to be that way.  When I was younger I played tackle football wearing regular shorts and even pants on occasion - it doesn't makes the game impossible to play.

There are sins in everything in the world - reject the sins and don't love the world love God.  

If somebody disagrees and believes that it facilitates sin and you should not watch it, I am okay with people believing that, I think that it errors on the side of caution, which isn't always a bad thing.