Bella loves the ball, but Baxter loves the Frisbee.
After a round or two (or three, or ten...) of catch with the ball, it was Baxter's turn to shine with the Frisbee.
He hasn't quite learned to "catch" the Frisbee, he sorta just lets us throw it and then he runs to pick it up. He's quite proud of himself, but it's very likely he's just glad Bella didn't get it first. If he was smart, he'd know that she really doesn't care that much about the Frisbee; her thing is the ball.
When she does pay attention to it, he sometimes let's her help him carry it back to us. While it looks like they share nicely, they really don't -- again, I think Baxter picks his battles.
Anyway, when all is said and done, you can tell they've had a tongue-waggin' good time.