There's no proof for or against God, just by the simple fact that God could just not care and not get involved, and such a God would be neither provable or disprovable.
The only position that can be logically drawn from that is the agnostic one: "I don't know whether God exists or not, and I don't care. It doesn't affect me.".
Atheists on the other hand are in a position that doesn't logically follow from the evidence. They believe that there is no God. It is a belief, because it cannot be logically derived from the evidence. And there are lots of Atheists who live their atheism like a religion. They study their literature to build a belief system, to find evidence, to disprove others. They meet up (online or physically) to talk about their non-belief and to hone their arguments. They strongly defend their position in discussions. I've even met Atheist missionaries who stand on street corners preaching that God doesn't exist.
To respond to your quote: Not playing tennis would be agnosticism. Atheists are running around the field, following the players and shouting in their ears that tennis sucks. They are playing, just a different sport.
I've seen a 3DS in the Technical Museum in Vienna.