They both have a play move that involves flipping over on their backs, and thrashing legs around happily. For those of you that know dogs, you know dogs don't flip on their back for just anyone, especially other dogs.
I used my 50mm f/1.4 on sports mode. Used the 50mm lens because it's my "fastest" lens in non-flash conditions, but the trade off is that it has a shallow depth of field; ie, focus happens at a specific distance from the lens, and all else will be out of focus. Some of the fuzziness is due to movement as well. I could use a wide angle lens, with greater depth of field (everything in focus), but out of direct sun and without flash (flash would distract pups from play, I assume, but maybe not?) there would be a lot more motion blur.