In the soccer scenario, as you say, the only choice to make is whether to participate. Whether to get hit by the ball can't be chosen independently. So the only

In the soccer scenario, as you say, the only choice to make is whether to participate. Whether to get hit by the ball can't be chosen independently. So the only opting you can do is playing (and getting hit) or not playing (and not getting hit). In that scenario, the default is to not play soccer. If you want to play, you have to choose it, i.e. opt to play soccer, i.e. "opt in". So the default is that you're "out". Thus, playing soccer is "opt-in". If people were born into soccer matches and had to actively try to escape, that would be "opt-out". You make a choice (opt) to escape out of the soccer match. Notice that "opt-in" and "opt-out" describe the inverse of the default value: "opt-in" is the same as "out by default" and "opt-out" the same as "in by default". Mixing these phrases with opposite meanings (e.g. "opt-in by default") creates confusion, perhaps intentionally, about what the default value is.