Soccer, or football (as it is called in every other country) is fortunately a versatile sport that can be played just about anywhere with a few meters of space.
For a little kick around without goals you can go to any park (Cascine, by the river below Piazzale Michelangelo, etc) or if you insist you need goals, you can head to some proper calcetto fields that you have to book and pay for. Those are located on the other side of the river at a place called Alberetta.
