cat that bites

Question
Why is it that my cat will come up and either bite my leg or arm for no apparent reason?

Answer
Attention seeking.  He's looking for a reaction, which we always give them when they bite!  We naturally respond with an "Ouch!" or a "What do you want?" or even just eye contact.  Unfortunately, these reactions encourage them to continue with the bad behavior.  So instead of giving him attention, negative or positive, place him in a cat carrier or in the bathroom for 1/2 hour, and ignore him completely.  It's the method that was recommended to me by two behaviorists when I consulted them about a biting Siamese.  That was 10 years ago, and I've used it to train a lot of cats since then.  It works if you enforce the rule every time he bites.  Some cats are easy to train, some are stubborn.  Some will learn right away, some will resist and may need a refresher course from time to time.  Depends on your cat's personality.  But I can say I have seen great improvement in EVERY case using this method.