Some putatively Knightian uncertainty and ambiguity aversion can be explained as maximising expected utillity when playing against an adversary.

For the Ellsberg paradox, the person offering the first bet can minimise his payout by putting no black balls in the urn. If I expect him to do that (and he can do so completely honestly, since he volunteers no information about the method used to fill the urn) then I should bet on red, for a 1/3 chance of winning, and not black, for a zero chance.

The person offering the second bet can minimise his payout by putting no yellow balls in the urn. Then black-or-yellow has a 2/3 chance and red-or-yellow a 1/3 chance and I should bet on black-or-yellow.

The lesson here is, don't take strange bets from strangers. I'd quote again the lines from Guys And Dolls about this, but the Google box isn't helping me find when it was last in a quotes thread. (Is there some way the side bar could be excluded from Google's search spiders? It's highly volatile content and shouldn't be indexed.)

In the tennis example, someone betting on the mysterious game or the unbalanced game is in the position of someone betting on horse races who knows nothing about horses. He should decline to bet, because while it is possible to beat the bookies, it's a full-time job to maintain the necessary knowledge of horse-racing.