When cats roughhouse, it's not always cause for alarm. It is natural for cats to play fight. Here are some signs that it's not trouble:
#1 Body Language
If playing, the ears should be in a forward or relaxed position. Sometimes in playing the ears may go back quickly but this is usually to try to keep them from getting bit. Tails can be thumping, swishing, still or thrashing. Claws might come out at times but are not being use as weapons.
#2 Body Position
While playing, cats will lean towards each other, not away.
#3 Role Reversal
One cat will likely lie on its side, inviting the nearby "aggressor" to ambush. during the play roles may reverse but probably won't be equally balanced.
#4 Time Outs
The cats will take time outs during play fighting; there won't be constant activity. They will pause several seconds to plan their next move or to switch roles.
#5 What Do You Hear?
Usually they will not be growling, hissing, or screaming. There might be an occasional hiss or shriek if one cat crosses the line and inflicts pain.
#6 How Did it Start?
About 35% of play fights start during grooming time. Other opportune times are when one cat is attempting to overtake a favorite sunning spot or when one cat is hiding behind a chair ready to pounce.
#7 Cat Fluff
You should not be seeing piloerection (hair standing on end) during play fighting. Sometimes the fur will get roughed up, but not standing on end, or with a brush tail.
#8 Biting Hard?
Sometimes during play fighting a cat will bite too hard unintentionally or when it gets excited. Typically the bite pressure is light to medium.
Play fighting can be part of a daily routine for cats who are friends.
#10 When Does it Happen?
Cats play fight when they are naturally more active and alert - early morning and right after dusk. Young cats might play any time of the day.