It seems to me that even if you know that there is a Doldun game, played by exactly two teams, of which one is Strigli, which game exactly one team will entirely win, 50% is as high as you should go. If you don't have that much precise information, then 50% is an extremely generous upper bound for how likely you should consider a Strigli win. The space of all meaningful false propositions is hugely larger than the space of all meaningful true propositions. For every proposition that is true, you can also contradict it directly, and then present a long list of indirectly contradictory statements. For example: it is true that I am sitting on a blue couch. It is false that I am not on a blue couch - and also false that I am on a red couch, false that I am trapped in carbonite, false that I am beneath the Great Barrier Reef, false that I'm in the Sea of Tranquility, false that I'm equidistant between the Sun and the star Polaris, false that... Basically, most statements you can make about my location are false, and therefore the correct answer to most yes-or-no questions you could ask about my location is "no".

Basically, your prior should be that everything is almost certainly false!