In Harry Potter and the Goblet of Fire, we see Alastor "Mad-Eye" Moody dole out punishment to Draco, by turning him into The Amazing Bouncing Ferret. Of course, later we learn that it wasn't really Alastor Moody, it was a poly-juiced Barty Crouch Jr.
So was it something ole' Mad-Eye would've done, or was it more Barty Crouch Jr. acting out revenge on the son of whom he probably considered a traitor?
It was most likely the latter; Barty Jr. was acting out on revenge.
Moody was a hard wizard, but still upheld the rules. He was careful not to break any, as he had spent years fighting to uphold them (being an auror). He wouldn't have used transfiguration on a student, no matter how much he hated him. This would've been like stooping to Umbridge's level, which I'm certain Moody would never have done.
There are several references to Moody being a cautious guy. He enforces even the most superfluous of rules like "elementary wand safety".
"Never you mind, you just keep your wand out of your back pocket!" growled Mad-Eye. "Elementary wand safety, nobody bothers about it anymore. . . .”
- Order of The Phoenix, Ch3: "The Advance Guard"
*(I used this specific excerpt because in most others, he is cautious because he's paranoid. But in this specific one, it shows that he cares about rules, even the small ones.)
Even later in that conversation he doesn't let Harry talk about Voldemort there at the Dursley's house. He's very cautious and one who plays by the rules. And after decades of auror-life, has become a very paranoid.
Hard to imagine someone who cares even about "elementary wand safety" would transfigure a student. And hence the conclusion.
Moody wasn't originally meant to be a nice and fluffy character in the first place, so it wasn't as "out of character" as it would be with someone like Lupin or Dumbledore.
Question: Can you give an example of a surprise in your writing process, such as a character you weren't expecting?
J.K. Rowling responds: Yes, it was a big surprise to me that Mad Eye Moody turned out the way he did. I really like him. I didn't expect to.
(src: "About the Books: transcript of J.K. Rowling's live interview on Scholastic.com," Scholastic.com, 16 October 2000")
Think of him as more of a Dirty Harry type cop... he's not at all concerned with shooting a bad guy dead, or roughing up a bully doing something bad.
No I don't think it was out of character. As Sirius says he was no villain, didn't believe in descending to the level of his enemies, but he was tough:
'[...] I'll say this for Moody, though, he never killed if he could help it. Always brought people in alive where possible. He was tough, but he never descended to the level of the Death Eaters. [...]'
Harry Potter and the Goblet of Fire - p.462 - Bloomsbury - Chapter 27, Padfoot Returns
He was hard as nails and he believed in tough justice, I think that's pretty clear from his words to Dumbledore in the Pensieve, just before Igor Karkaroff names names.
'Crouch is going to let him out,' Moody breathed quietly to Dumbledore. 'He's done a deal with him. Took me six months to track him down, and Crouch is going to let him go if he's got enough new names. Let's hear his information, I say, and throw him straight back to the Dementors.'
Harry Potter and the Goblet of Fire - p.511 - Bloomsbury - Chapter 30, The Pensieve
He may not have been unscrupulous, but I don't think he'd have had a problem with Crouch Junior's "teaching".
Yes, it was out of character. "Mad Eye Barty" was beating Draco. Mad Eye Moody would not "use transfiguration as a punishment"; Mad Eye Moody would not abuse a child.
Mad Eye Moody respected rules and Dumbledore. Nothing in his character or experiences suggest he would harm an innocent.
