That’s not comparible though: you’re mixing US domestic with international.
Now, if the Ireland or England national American Football team went into a global competition that involved most countries in the world, and we were playing the USA national Football team, then it would be the same deal. And quite a big one. (It would also probably result in the extinction of the entire Ireland and England team members. ;))
Rugby is not really a ‘big world sport’ - its popularity is mainly concentrated in (i) English-speaking countries outside North America and (ii) France.
I wonder what is the world’s second-favourite team sport? Baseball or basketball, I’d guess.
I think the main difference between the US and world sports is the flow of the game; American football, baseball, basketball seem (to me) to be very stop-start games - there seems to be a bit of high paced action, then a pause, then more action, etc. The world sports (soccer, rugby) seem to be more flowing with not nearly as many pauses.
I also think that the difference in strategy levels that Ellis Dee describes is based on lack of knowledge of rugby and football.
Well if you stretch the definitions of Americans to also include Canadians. It’s certainly not in the top tier of popularity, but there is more exposure here than in the States. Especially on the west coast. We have pretty good coverage here on the cable sports channels. I got to watch all the tri-nations and super 12, and now the world cup. Sadly we got trounced again yesterday.
Soccer is also getting fairly popular. Three world cups ago, I was in a tavern in small town nothern Alberta (<2000 population). I asked them if they were going to show the game. The bartender looked at me like I was an idiot and said “of course we are!”
I find American sports are more explosive. During a play, everybody is going at 100%, but consequently, there have to be more breaks. You could not keep up the pace of American football during a play continuously, whereas in soccer and rugby, if you’re not in the immediate play, you can often kind of dog it for a few minutes to catch your breath. Both styles of sports have their challenges.
How do you explain Japan, Uraguay (yes i know i ccan’t spell that), Tonga, Samoa, France, Italy etc then. I’m not a huge fan myself. But I would think as far as numbers of countries rather then population, rugby would have to be second after soccer.
RE: the OP, I would say that rugby has less than 1% of the following that soccer does in the US.
I don’t have cable TV so I can’t say what channel it is (or isn’t) on.
Personally, I just can’t believe we need MORE sports than we already have.
You could get rid of a few like tractor pulling etc. 
This coming from a country where a big news story was the National Ploughing Championships a few weeks ago
Well they can always rustle up a few minnow teams to make up the numbers. Even the Rugby League World Cup managed that, just about. But I don’t think rugby (Union) is big in Japan (to coin a phrase) or Italy. Possibly the no.2 sport in Argentina, but a long, long way behind footb… soccer.
I am presuming that you mean for football - or what you call soccer - to be the world’s number 1 sport.
I would say that there could be little doubt in anyone’s mind that cricket is the world’s second favourite team game.
Or is that not a “big world sport” either?
What is a “big world sport”, anyway?
Surely a global competition where the national teams from countries of every continent compete is big enough and worldly enough for such a definition?
What’s Rugby?
Kidding of course. Had no idea the US had a team though.
Well they can for popular sports
Like I said I would think Rugby would be the number 2 sport in a lot of countries. Of course I say that coming from somewhere where it is number one.
Yeah, cricket, you’re probably right, what with its popularity in India and thereabouts. Of course, we’re arguing over the definition of “big” here - I was nitpicking Ellis Dee’s description of ‘soccer’ (a word I certainly don’t use, btw 
) and rugby as ‘the two big world sports’. I mean the sport having the most spectators, or people who follow it closely.
What yojimbo said, plus:
My impression is that the major differences are related to individual intiative and stamina (commercial breaks notwithstanding).
In rugby and association football there are no “special teams” coming on just to kick the ball.
Certainly there are players with special responsibilities and talents (Wilkinson and Beckham for example) but those players are also expected to pull their weight and perform as part of the team.
There are no lengthy breaks and time-outs during play (except for injury), and there are no opportunities for the team to plan each move in detail. Some moves are planned and practised in advance (set pieces such as corners and free kicks), and tactics are reviewed and established before each game, but much of the action is determined by individuals reacting to the flow of play.
rankings - by national participation
basketball (208) - the FIBA site lists 208 national federations as members
association football (204) - FIFA lists 204 affiliated national organisations
baseball (112) - the IBF lists 112 full and provisional countries and territories, and controls the Baseball World Cup (first hosted in 1938 by Great Britain, and won by GB)
rugby (94) - the IRB world rankings list 94 countries
cricket (37) - the ICC has 10 full members and 27 associate members (including the USA)
american football (20) - the IFAF lists 13 full members and 7 temporary members
there are also 201 National Olympic commitees
I think here in the CA bay area it is only available through a “pay-per-view” service, which sucks because I would love to watch. 
I can certainly appreciate the overall talent of these players, and I’m a huge fan of soccer and rugby.
On the other hand, if the play is planned beforehand, like in American football, I prefer to watch the people who are the best at that type of play than somebody who may be good overall but not the best.
Say you were interested in track and field. Who would you prefer to watch, decathaletes, or the world’s best in each event (not considering that these groups may overlap)?
Well, I watched New Zealand and France play this past weekend on Fox Sports World for about 10 minutes. I didn’t realize it was the Rugby World Cup. And I certainly didn’t know that the US had a team, but I guess it make sense since a lot of universities do play it at the club level.
So it’s on, but no one much cares. Baseball playoffs are going, with the Cubs trying to reach the World Series since the first time in nearly 50 years. And win it for the first time in 95. And Boston and New York are going at it in the ALCS. Plus, American pro and college football are going on. And the NHL season just started, but to be frank, that’s a distant fourth on American professional sports radar. It’s really not even close.
It’s all a question of personal choice, you prefer the team to be able to bring specialists onto the pitch for a particular play, and I prefer to watch a free-flowing game in which the specialists are an integral part of the team. And in matters of taste there can be no argument - everybody is right.
Just for the record I am not trying to knock any sport, I have watched and enjoyed most US sports including American Football. In fact for a while I supported the Redskins (probably because I read Doonesbury).
As for track and field, I would watch both the individual events and the decathlon, they are hugely different events because of the wide range of abilities the decathletes have to display.
I don’t think it’s college kids on the teams. Most guys (women, too) don’t even LEARN rugby until college. There are city club and regional teams, and I assume (?) that’s where the U.S. Team players come from.
Rugby is not well known in the U.S., but the people who play and who follow it are in a rather close-knit community. That is, if you play rugby in Milwaukee and then move to Boston, all you gotta do is find the ruggers and you’re set. Like a fraternal organization. The better players from across the country all know each other from playing on the regional all-star teams and seeing each other at tournaments.
I wish rugby were better known and more appreciated. It’s a beautiful sport to see played. But … on the flip side, with popularity would probably come a loss of that sense of community.