This was a whole new ball game. But only because it was a new (different) ball, since this was fundamentally the same basic game: maintaining exclusive possession of an inedible object and depriving a contender of possession. 

About four weeks after the immature adult took off with the dog's blue plastic ball, an almost fully mature eagle dropped in and took ownership of a different toy, a tennis ball. This time possession was contested by an immature adult. It might have been the same one that had prevailed in the earlier dispute (since the neck feather patterns seemed similarly distinctive).

There was the usual show of challenger intent: approaching at a crouch, moving into close proximity to the possessor and the prize, some posturing with raised wings, and finally a show of indifference as though to indicate it hadn't really wanted that prize. And there was the usual show of possessor intent: clutching the prize with talons, brief flight with a flurry of powerful wing beats to gain altitude and ascendance, lowered-neck inspection with wings partly extended, decisive talon-grabs, displays of the prize grasped (provocatively) by beak, another lift-off to demonstrate dominance, a little extended-wing posturing, and finally, after a crouching launch, departure with the ball firmly grasped.  The ball is hidden in the two final flight pictures because the talons and ball are tucked up under the tail feathers.

The ball wasn't much of a prize, although its surface fluff might have seemed useful for nest building, and it was clearly inedible. Again, the real game seems to have been confirmation of dominance as reflected in denial of possession to a contender. If in fact the unsuccessful contender had prevailed in the earlier contest, it might reflect something of eagle willingness or reluctance to relinquish possession of an inedible "prize." At least one study implies that changes of possession of food items turn on the relative aggression displayed by the possessor and the contender, and how each one assesses the other's aggression and willingness to engage in actual physical fighting. The study suggests that, assuming adequate food supplies, the hungriest eagle will prevail because the possessor, already at least partially satiated, knows the challenger is more desperate and more likely to actually fight. In context of inedible items, perhaps the possessor realizes the challenger is motivated by mere curiosity, not hunger, and isn't likely to fight. The possessor consequently can make aggressive possession displays, assuming the challenger is not willing to fight. 

By the way, this ball never reappeared.

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