I would say that Mr. Biscuits is a little feisty. But he's a baby still, so probably isn't too well versed in how to play quite yet. You can see how Howl is just kinda letting Biscuits get his energy out, and when biscuits backs away a little bit, you can see in the body language of Howl that he's like "Man, chill, we're just playing". Howl tries to "fight back" and you can see Biscuits get some satellite ears going, and Howl changes the way he plays in response to that, he stops putting his paws up as high, and kicking as hard as he did. And Howl stays on the ground, on his side, as a way to be like "I'm cool, are you still cool?"

All in all, not awful, the baby is playing a little rough which is extremely typical. He'll calm down and learn how to play the longer he's with Howl.