We here at Fish School have focused mostly on training individual fish to do tricks, sometimes in the company of other fish, but not (yet) to act as a team. But if video of Koi playing soccer below is any indication, a team version of soccer (i.e. what everyone else in the world calls football!) should be very possible. I strongly suspect these Koi weren't even trained, but are instead just doing what comes naturally.
As you can see from the picture of Comet, the Koi soccer (with its floating ball) bears a striking resemblence to the basketball trick that comes with the soon to be available R2 Fish School Training kit. Of course the R2 training kit we helped design comes with a hoop, to give you fish a concrete target to shoot for.
And as you can see from this picture of Comet playing soccer, our version of soccer comes complete with a sinking field, goal, and realistic ball. Much cooler, and more fun!--Dean