Whether you are stopping or changing the bad guys or helping the good guys, we need data to understand patterns and effectiveness of our tactics. This idea uses low level technology (radio waves) and relies on children playing soccer...
James - love this idea as I feel that sports prove a universal means to bring disparate groups of people together. Along with seeding the concept with already organized local sports teams, organizers, etc. Nike could create brand ambassadors (as they do in other parts of the world) that earn points for organizing events, playing in games, etc. Very simply done - the more you organize, the more points you get that can be redeemed for Nike gear (which is another form of Nike advertising, so they are fine with that).
In addition, the idea of keeping stats on some level is great. People love seeing where they stand among a group because it affords them the opportunity to move up and improve, proving to them that they are providing value. However, must be careful with making this too competitive if you have some sort of "Player Card" so that you don't run into the problem where people don't want someone to play because they are terrible (based on their "Player Card"). A solve for this: Player Card is based around events organized, attended, etc.
Lastly, for those who don't play sports, is there a watching element to this as an auxiliary piece? On your site can they go through the filter of "Play" or "Watch", then the "Watch" would be organized get togethers at local pubs with a specific game on.
Tapping into active community members to help spread the word within their community is a cost-efficient means of spreading the cause and keeping it alive past 1 single event. What incentive can be given to these early adopters encouraging them to bring their friends to events and help spread the word? Not living in Singapore, I struggle with this answer, but perhaps some form of "social cash" (recognition) at the events.
In addition, if the events are taking place in areas where community members pass on a regular basis, would it be possible to leave something from the pop up events? This way these events would literally leave a small mark on the community that continuously invites curious passer-bys to stop and maybe seek out more information. If space is at a premium and smart phones are prominent in the area, this could literally be a bar code w/ a curious sign where a video or pic from the event is brought up when the bar code is scanned. This will allow for a continuing stream so the community is creating a story thread through these events.