Tommy's defense is many-layered. Like Shrek. It goes as follows:
1. I didn't steal anything from George Lawrence
a) but if I did, it was because the bit of cloth just liked me more. Tampa wasn't cherishing her! They were just leaving her laying around in the corner of Clay's room, collecting dust! I named her and made her into a pocket for my backpack and I should not have to rip all the seams when they weren't using it anyway, not that I took it, because I didn't, that doesn't sound like something I would do, this is mine and you can tell because it is on my backpack
b) also how was I supposed to know it was George's and not Clay's, why does George leave his stuff in Clay's room, that's fucking weird, are they dating or something
c) "stealing" is such a harsh word. Terrence and Wilbur would have called this "redistributing wealth" and/or "based", maybe everyone else just needs to adopt a more positive mindset
d) and maybe it was going to go bad and kill George. Lots of things do that, in the Scholomance. So really, if you think about it, he saved George's life, and instead of being punished, they should reward him.
And, just as importantly:
2. Lying is bad, unless you can get away with it. Then it's probably fine.
So when Toby comes up to him to say that some of George's fabric is missing and Clay suspects him, he says, "That doesn't sound like something I would do."