It would turn into a game of defending your opponents goal to prevent them from scoring on themselves. Actually if you think about it, it could add a whole new element to the game and maybe even be exciting, if not more confusing...

From the strange but true files: the Caribbean Cup once had a rule that awarded a two goal victory to teams that won in overtime, so Barbados scored an own-goal against themselves to create a tie that would force overtime. Once their opponent figured out what had happened there was three minutes of football in which one team was trying to defend both goals against another team that was just trying to make sure the game did not end in a tie.

The "suicide" strategy is much harder to pull off effectively. The team to go to that strategy would need to "win" by more than five goals. If the other team can score only enough to keep the difference less than five, then they win by the regular rules.

This would mean that a team attempting the "suicide" strategy from the outset would need to be much better in that paradigm than the other team. If we assume that the skills involved are similar, this would mean that they could probably win anyway using the normal rules. Adopting the strategy partway through the game -- say, when behind by three goals -- could be effective, but if the other team knows about this, they would keep the difference to only two goals.

It would result in either a heavy emphasis on defense, or a strategy of scoring one goal and then passing the ball around for the rest of the game.

There is one problem with your analysis. The team that gets scored 'on' is the one that gets the ball for the kick-off.

Since different teams get the initial and half-time kick-offs, it boils down to which team is capable of scoring the most own-goals in the same (lengthy) amount of time. The second team has a huge advantage, because they win by scoring 4 less own-goals than the leading team.

It would turn into a game of defending your opponents' goal to keep them from scoring and attempting to score in your own goal. It's like real soccer, only goalies can only pick the ball up when they're trying to score.

ah, the misere game. http://en.wikipedia.org/wiki/Misère

Modify the rules so scoring in your own goal doesn't count?

Without modifying the rules, you could effectively reverse the game into a race to score goals in your own goal. Goal keepers would be the strikers (much more effective strikers since they can use their hands). Most players would be just trying to control the ball and move it towards their goalie/striker

Awesome. I wish more opportunities for exploits like this would open in sports, the games would take some interesting intellectual twists. Oh wait, we're playing calvinball.

Ultimate frisbee captains can, I believe, agree on any subset of rules before a game begins. The inclusion and use of dodgeballs on the field was one modification of note.

There are lots of them. One enterprising swim coach figured out that you could swim breaststroke much faster if you brought your hands forward above the water instead of under it. This'hack' gave birth to the Butterfly Stroke.

Another figured out that swimming upside-down under water was faster than back-stroking above the water. Alas, this innovation was banned. And so it goes.

Politics gets into it, as anyone who followed the UCI's wars with Graeme Obree would remember:

http://en.wikipedia.org/wiki/Graeme_Obree

Slight technicality--goalkeepers can't use their hands if the ball is passed back to them by their own team.

This league would be better off modifying the rules so that every team finishes undefeated by default.