Good question. Football is clearly number 1, in both watching and participating (team sports, that is, I know there’s loads of people who ‘run’ so that’s probably the actual #1 participation)
Rugby i would guess is #2 – certainly if you combine codes but people’s relationship with watching rugby is different to football.
Cricket probably number 3, but not sure on that and in terms of watching, there’s another massive difference.
I’m not sure in terms of participation – there are for example lots of hockey clubs, often running several teams. lots of people play ‘recreational’ netball, so not particularly leagues or tournaments like football but just various teams meeting up each week and playing against each other for fun and exercise. Basketball’s another; not many clubs playing league but a very vibrant 3v3 scene in some cities.
The watching thing is odd. Football, it’s almost all about clubs, and most football fans have club way above country in priority. Of course you want them to do well when they play but the rest of the time it’s in the background. Most football fans can tell you who’s doing well in the Premier league even if they support someone else. You can name managers, key players, etc. I’m racking my brains to even remember who’s in our group at the WC in the summer! And most England games are not sell outs, whereas getting a ticket to a PL game is frequently impossible.
Compare to rugby, which is a hybrid. Proper fans will know teams and players but the causal fan, like me – despite watching games on TV if they’re on I couldn’t name the top 5 in the Premiership with any certainty. Games will usually be to full house or close to full house crowds (exception the football ground shares), but stadiums are often a few thousand, maybe <10K? But try to get tickets for a 6N and it’ll be tough.
And then cricket. Tickets for tests and internationals are generally hard to get hold of (at least require planning and purchase generally well in advance, certainly in England and depending on who against obvs) But club games, particularly the Championship, are often taking place in front of a handful of spectators. And i consider myself a cricket aficionado but the county game does nothing for me – i can’t even tell you who won it last year (I know it was Yorkshire the season or 2 before but only because Jason Gillespie was coaching)