I've had Missy out at the dog park a couple of times now, and she is a huge ball fiend. She can barely sit still waiting for you to throw the ball and takes off like a rocket after it. She's a lot of fun to watch chasing after the ball.
She even brings it back to me, unlike some dogs I know (Nala and Simba, I'm looking at you...)
This makes it easy to tire her out. She also doesn't know when to stop and take a break. Now that it's getting hotter out, it's easy for her to run herself into heat exhaustion or worse, which is bad, especially being a black dog and smaller than the others, who do have the sense to stop when they get too hot. That means rationing the ball throwing and making her take breaks, even though she looks like she doesn't want to.