Rojo, great idea for a thread because this is something that has annoyed me.
First I will assume based on an implied contract and precedent that the fan who caught the ball owns it. (A court could decide if that's true or not)
Second, if I was a multimillionaire team owner or player I would NEVER have the selfishness or lack of sensitivity to ask the common Joe fan to donate the ball to me. I just wouldn't do it. The fan is put in a situation surrounded by a famous athlete and team representatives and media that put very strong yet implied pressure on him that its the "right thing to do". No one of course suggests to the fan that he might want to think about it overnight. No, they sweep the fan away and lead him to make a decision in the moment. Its unfair.
Even if the fan is wealthy and has no need at all for the money, its still probably is a bad choice to give the ball back to these multimillionaires. The decision comes down to what charity is the most worthy for him to donate this very valuable ball. Should he donate it to these multimillionaires or should he donate this to a worthwhile charity such has people who have lost homes in war or floods, or people who can't feed their children.
Its an easy decision.