You are describing the exact behavior that my Shamrock has. He is
a leg biter, and bites out of the blue (not from overstimulation
unless just looking at him overstimulates him, though he also has
the classic overstimulation biting).

I've had him for over 2 years and haven't solved this problem yet.
I've sort of gotten used to it, though he can bite hard,
especially when I'm getting his food ready, or I'm stepping in the
shower. For a while he really scared me because I couldn't walk
across the room without him attacking my legs and I would always
have scratches and bite marks on my ankles and lower legs. I used
to carry a laser pointer to divert him, and this worked well.  He
isn't nearly this bad anymore, but he still has his moments. Some
cats just seem to be like this, and otherwise he is a very cuddly,
nice cat. Sometimes he seems like he really wants to be pet, but
you can't touch him in certain places. There only seems to be
about a 2 sq inch area around his head that isn't off-limits, and
only *sometimes*. lol

I've come to the conclusion that he thinks I'm a big cat because
he treats me the same as he does my other cats.

As an aside (which is probably very relavent) Shamrock has
allergies that cause his skin to erupt in lesions, and can only be
relieved by steroid shots. I attribute his behavior sometimes to
just being itchy, grouchy and possibly in pain at times. In all
this time I haven't been able to find the allergen but I think I
might have found it because he is doing very well after a recent
(yet again) diet change.

I had a cat do this. He'd bite me when I'd arrive home from work and didn't pet
him "enough." He basically wanted me to play with him more because he was bored
and lonely. My cat would sometimes bite if I spoke to someone else or was not
petting him when he felt I should be. I just decided to give him tons more
attention. I'd play with him with a toy dangling on a string. I'd try to tire
him out. Sometimes I'd even pet him "too much" so he'd get off my lap. I think
your cat just needs more attention and play time when you come home from work.
Think of it as wind down time for both of you. He'll get better as time goes
by. Did he used to live with another cat and get along with that cat? If so,
maybe he needs a buddy to keep him company when you're at work. Don't get a
kitten. Get an older cat IF he used to enjoy other cats. If not, just play with
him more when you get home.

It sounds to me as if he's correcting you. Twice you were walking away and
twice he bit the hand NOT petting him.

He wants more attention or interaction, and he's correcting you for not
giving it to him. He may be used to being the boss.
My personal opinion is that *I* am the boss in my home. My critters get away
with a lot (they're quite spoiled), but I put my foot down for some things,
especially biting or aggressive behavior towards me or any other animal or
person in my home. If this were my cat, I would immediately correct [1] *him*
after the bite and then give him a timeout for 10 minutes or so. He doesn't
get to tell you that he wants attention - he can *ask*, but he better not
*tell*, if you get the distinction.
I don't know how much you play with him, or how much he was used to, but he
may just really need more stimulation. It's one thing to correct him, but it
doesn't solve the underlying issue. He may just redirect into destroying
property. You want to solve the real issue while still making sure he
understands that hard biting is NEVER acceptable. Either spend more time
playing with him or perhaps consider a second cat to add to your home. It is
my opinion (and experience) that 2 cats are nearly always better than one. A
few cats simply won't accept other cats in their territory. Most, however,
like the company.

Of course, I assume since you mentioned the vet that he has already been
checked for health problems. Health problems should always be ruled out
before assuming the issue is strictly behavioral.

[1] By "correct", I do not mean to hurt him. A light scruff shake (just a
firm grab of the scruff with his weight still on a solid surface - do not
pick his weight up by his scruff, ever), a nose tap, or even a just a loud
booming NO should suffice. Some cats hate getting squirted with water. Others
hate loud noise. Any aversive will do. You want his respect, not fear.
Note that, occasionally, bossy cats may react with further aggression
(hissing, spitting, swiping, or more biting) when corrected. If he does this,
STOP. You don't want a battle. You'll both lose in the long run. Stick with
positive motivators to shape desired behavior and timeouts as punishment if
he reacts aggressively to corrections. You may want to consult an animal
behaviorist if he responds aggressively to corrections. One size does NOT fit
all in animal training.

While she never broke the skin, one of my cats used to bite the back
of my leg if I wasn't giving her the attention she wanted.  It was
almost always when I was at my computer, where I have a can of
compressed air handy, and she hates that noise... she doesn't bite
very often anymore :)

--
Jennifer

<snip story of cat biting>
From the scenario you decribe, it sounds to me like this cat is acting
out because he is partly stressed from the changes in his life, and
partly because he is bored and has built up energy that is expended as
aggression towards you. There are a couple of things you can do to
minimize this behavior, and over time eliminate it if you are very
consistent, although it will probably take awhile to do so.

Ignore the advice Kaeli gave you to "correct" this cat with scruffing
(Kaeli should be ashamed of herself for even suggesting such a thing.)
The cat will look at this as an aggressive action, which will cause a
fear based reaction, and will only make things worse. Physical
corrections should NEVER be used. EVER.

The best solution would be to adopt a second cat as a buddy and playmate
for your cat. Not just any cat will do. In this situation your best bet
would be to find a male that is similar in size and activity level, very
playful, but with a laid back, tolerant personality. Making sure to do a
very slow introduction is key to these two forming a friendship. You can
read how to do that here:
http://www.catsinternational.org/articles/getting_a_cat/good_introduction.html

Even if getting a second cat is not possible, you need to do some things
to keep this cat mentally stimulated while you're away and develop a
routine at home that gives him something he can count on.

One thing I always do is leave the radio on set to a classical station
on a low volume 24 hours a day. This has a calming influence and hearing
different music and calm voices throughout the day is an easy way to
keep your cat's mind busy.

Providing him with a nice, *tall* cat tree he can climb and play on and
placing it in front of a window so he can watch the world go by is
something I would definitely recommend as well. You can see an example
of one of my favorites in the last photo at this link:
http://community.webtv.net/zuzu22/scratch

If possible you can make this even more enjoyable for the cat by putting
a bird feeder outside the window where the cat tree is.

You also need to take steps to take your cat's focus off of you as
"prey" and send him in another direction.

If your cat will chase the dot from a laser pointer carry one with you
when you're home and when you see him getting ready to come after you,
send him off after the dot instead. When purchasing a laser pointer
you're better off buying one that takes AAA batteries as they last much
longer and the batteries are cheaper than the kind that take watch
batteries. I've found great deals on this type of laser pointer on Ebay,
and I have seen one at Target for $10 that is in the section where they
have labelmakers, etc. It looks like a thick, silver pen.

Getting him one or two stuffed animals that are a little smaller than
him are also useful as you can throw them to him when you see him
setting up for the biting behavior and he'll likely grab the toy and
bite that instead. This will take the focus off of you and teach him
that he can beat up the toys as much as he wants. Getting him to beat up
the toys when he's not in attack mode will also teach him that they are
acceptable outlets for his aggression and will also expend some of his
energy.

Keep a few little containers with treats around the house, and if you
see him setting up to attack, grab the container, shale it,then takea
treat and throw it in a different direction. Again, this changes his
focus, gives him something positive, and also the opportunity to chase
something and expend energy.

A wand with feathers on the end is also useful for redirecting his
aggression from you to something more appropriate.

Setting up a regular play session with your cat each evening shortly
after coming home will help, and if you do this at the same time each
evening, and you've taken steps to keep your cat's mind busy during the
day, your cat will quickly fall into the routine and probably will stop
the biting behavior when you walk in because he knows what's coming in a
little bit. Routine is very comforting for cats, and even things like
scooping the litter and feeding meals at the same times and order each
day, or doing your own routine in the same order each day, can help a
cat feel more secure.

Also keep in mind that many cats don't react well to change and will act
out aggressively. Your cat spent several years of his life in another
home with someone else, and having to adjust to a new home and a new
person is a lot to have to deal with, especially when they don't know
why this is happening to them and are totally at our mercy. It can take
a lot of time for a cat to get used to new people and new surroundings,
and underlying fear can certainly manifest as the behavior you describe.
Don't be angry with this cat. Understand what he is going through and
take steps to redirect his aggressive behavior and make him feel that he
is a part of your home and all that happens and over time this behavior
should greatly diminish and hopefully go away.

Megan