Play or fight?

Not only do they look like they're not really trying to do any damage to each other, they also seem pretty relaxed after disengaging. But I don't have two cats so I may not be the best judge.

These aren't my cats but it shows that cats can get into it pretty good and quite a lot of noise and still be playing.
Also shows just how fast cats can be.

Another good one.
Just don't like how they filmed it

Definitely play time

It looks like a little "domination tiff" to me...Longhair is sparring and trying to dominate the shorthair, but the shorthair actually "wins" the tiff by pinning the longhair. No serious fighting going on here.

Serious is when you hear truly awful shrieks and see a ball of fur tumbling around with fur clumps flying.

Our two Maine Coons go at it every morning but it's all play. It starts with a game of chase up and down the stairs and then a wrestling match on the bed. It's quite entertaining to watch.