Rodent tough guy

Hi All;
I saw the most amazing thing looking out the kitchen window the other morning.
Unfortunately, I did not take a video of it.

We have two young outdoor cats. Both boys and both fixed.
They are constantly hunting,  rats, mice, birds, snakes... I even watched one try stalking a herd of wild turkeys.

The other morning I observed Sammy, terrorizing/playing with an adult mouse... (I thought)
He was tossing it up in the air and then pouncing on it... typical kittie behavior.
All of a sudden, I see the "mouse" up on its hind legs attacking/ defending itself! Who knew???
Of course, Sammy was not impressed, a few more bats with his paw and then it was time to have a nice mousy snack.

I have never seen such a thing!  I now suspect that it may have been a teenager pack rat rather than a field mouse...  
Lucky, he did not get his sword out before Sammy finished breakfast!

Any chance it was a shrew? They can be quite aggressive, are about the size of a mouse, and have been known to attack animals much larger than themselves.