EV3 is a robotics sets from LEGO Mindstorms. With EV3 you could build an infinite number of robots like Vehicles, Animals and Tanks. The set comes in two parts - base set (45544) and a resource set (45560). EV3 robots are very popular at LEGO Mindstorms Robotics Competitions
Here is Mintonet. The robot is created to be used in pairs, but you can also build just one and practice your shooting with a box. The robot works with plastic balls between 5 and 7 cm. Using the ultrasonic sensor it can detect either its partner or a box and then it shoots. How many balls can you score?
Football with robots could be quite fun. Football with LEGO Mindstorms robots is one of the popular categories for competitions with LEGO Mindstorms Robots.