Definitely playing. If it was fighting, one would be cornering the other and there would be fur flying. And lots of welping, crying or yipping.

Its playing because:

1) Body language: Tails are wagging; theyre not going head to head biting each other- theyre biting and then turning around and following each other, and then pausing, and then going back.

2) Tori would never roll on the floor like she did if it was a fight.

3) There's no blood... No cuts... No missing fur...

Eli and Bunny play like this as well. They'll get each other on the ground and bit legs. Bunny really naws away on Eli's legs but it doesnt seem to bother him. When dogs fight, its very obvious. There's no doubt.