While reading
this story a while back it occurred to me that it really doesn't matter if a sport is played on a perfectly uniform and unobstructed pitch or ground, as long as the teams change places in such a way that any obstacles introduced by the environment are borne in the same way by both teams for an equal proportion of the game.
So how about this for an idea - Forest Soccer! Or 'Foccer'. I'm going with 'Soccer' here rather than 'Football' because I see this idea taking root in the USA. European and South American countries wouldn't defile the beautiful game like this, but Americans will defile anything up to and including other people's countries, so they'll be on board.
I don't think there's a particular size a soccer pitch needs to be in order to confirm with regulations, so let's say 100 yards by 50 yards. You pick a piece of terrain - the name suggests forest, but you could use a rocky area, watery, whatever - and mark out a 100x50 area within. Then this becomes the pitch and all other rules of the game remain the same - you can't, for example, take the ball outside of the boundaries of the pitch.
Let's say you're playing in a rocky area and because of where you've placed your markers, one of the teams' goalmouths is actually buried within ten feet of cliff-face and isn't actually accessible unless you use tunneling equipment. No problem! The teams will both have to deal with the fact that their opponent's goal technically doesn't exist for the same amount of time during the game (I suppose you could play silly buggers with the extra-time rules, but existing penalties for diving, timewasting etc. will still apply) because of the requirement to swap ends after 45 minutes.
And the presence of, say, a forest on your pitch means that players can attempt to use the obstacles to their advantage - perhaps a defender can smack the ball into a tree so it gets stuck, and the attackers then need to climb the tree to get the ball back (but they can only touch the ball with their feet which makes it extra challenging). Or perhaps you can play a silky pass to yourself by bouncing the ball off a tree. You could coerce a local badger to savage the opposing team's goalkeeper - free shot!
I'm using soccer because it's most familiar to me but you can do this with other sports too, as long as there's a change of ends. For example, instead of beach volleyball, why not 'marsh volleyball'? Or urban tennis, played with each player on a different rooftop - be careful when coming in to the net. Ice hockey in a desert. So many possibilities.