Very often when a cat has been involved in a fight the owners will be aware of it, either due to actually witnessing or hearing the fight, or because they can see visible wounds on their pet.
The teeth and claws of a cat are capable of inflicting deep, penetrating wounds and unfortunately they also carry many harmful organisms into these wounds. The teeth and claws of the aggressor may also remain inside the victim! This can lead to the formation of an abscess following a proceeding cellulitis, (an infection of the tissue).
If you suspect your cat has been involved in a fight, and especially if you are aware of any wounds following such an incident, it would be wise to consult your vet since early antibiotic treatment may be able to prevent the formation of an abscess. If you are sure that the wounds are superficial (beware small roundish wounds especially if there is more than one - they are very likely to be bites and be deep puncture wounds) then you may decide to "wait and see". In this case you can try to clean the wounds if you wish. I would suggest using warm, salty water and it may be helpful to clip the fur away from around the wounds. Do take great care since horrible injuries have been inflicted upon cats by caring owners attempting to clip fur and actually clipping skin! Also take care not to get bitten or scratched yourself. If in any doubt regarding your ability to do these things leave well alone!
If you do decide to adopt the "wait and see" approach following your cat being involved in a fight, watch out for the following signs that your cat may be developing a subsequent infection: lethargy, not eating, pain (limping, crying out, excessive grooming), lumps or masses which appear on the body, discharge of pus or blood, wet looking areas of fur, or any other sign which is unusual for your cat. In these circumstances do not hesitate in contacting your vet.
See also: abscesses in cats.