Given that he and several other Death Eaters (namely Bellatrix, Rabastan and Rodolphus Lestrange) had attacked the Longbottoms, with four people attacking two, why did Barty criticize Draco Malfoy for attacking Harry Potter from behind in The Goblet of Fire?
If attacking someone from behind is cowardice, then how is a four on two fight any better?
Barty had a bone to pick with Lucius Malfoy and Draco served as a substitute. That was the reason of the memorable ferret incident.
The fun part is that Barty didn't need to feign hatred. He was genuinely angry with prominent death eaters like Lucius Malfoy who after the Dark Lord's disappearance denied culpability, claiming that they were compelled by the imperius curse to assist Voldemort:
“He forgave them, then?” he said. “The Death Eaters who went free? The ones who escaped Azkaban?”
“What?” said Harry.
...
“I asked you,” said Moody quietly, “whether he forgave the scum who never even went to look for him. Those treacherous cowards who wouldn’t even brave Azkaban for him.
...
“I told you, Harry… I told you. If there’s one thing I hate more than any other, it’s a Death Eater who walked free. They turned their backs on my master when he needed them most. I expected him to punish them. I expected him to torture them. Tell me he hurt them, Harry…”
~Harry Potter and the Goblet of Fire : Chapter 35 - Veritaserum
Barty wanted to hurt those unfaithful. And here he found Draco, a carbon copy of his father, attacking Harry Potter, which gave him a good excuse to have a bit of fun behind the mask of the eccentric Auror:
Malfoy, whose pale eyes were still watering with pain and humiliation, looked malevolently up at Moody and muttered something in which the words “my father” were distinguishable.
“Oh yeah?” said Moody quietly, limping forward a few steps, the dull clunk of his wooden leg echoing around the hall. “Well, I know your father of old, boy… You tell him Moody’s keeping a close eye on his son… you tell him that from me..."
~Harry Potter and the Goblet of Fire: Chapter 13: Mad-Eye Moody
As the real Moody also had a couple of good reasons to despise the death eaters (what with him being an auror who lost comadres and was injured countless times fighting them) Barty could easily stay in character and show his hatred towards the Malfoys, Snape and Karkaroff, without arousing suspicion.
Very unlikely that Barty was truly revolted by Draco's sneak attack, as his purpose was to deliver his underage student to Voldemort's hands, also as sneakily as possible.
Barty Crouch Jr. didn’t necessarily actually care that Draco attacked Harry when Harry’s back was turned. (It’s possible, though, that he did, but either considered an opponent with their back turned different to being outnumbered, or was simply a bit hypocritical.) However, it would certainly be believable that Moody would care about something like that. Barty was playing a character, and for him to be able to take any action, especially so publicly, it would have to be something that Moody would plausibly do. To turn Draco into a ferret, he’d need a reason that people would believe for Moody to do it.
It was certainly in Barty Crouch Jr.’s interest to keep Harry safe, and therefore stop Draco before he could do any serious damage - he needed Harry to be well enough to win the Triwizard Tournament. He couldn’t afford Draco possibly doing enough damage to Harry that he wouldn’t be able to win and fall into the Dark Lord’s carefully set trap. He explains to Harry that he made sure to scare off anyone that would hurt him or possibly stop him from winning the Tournament, which would include Draco trying to attack him from behind.
“Who put your name in the Goblet of Fire, under the name of a different school? I did. Who frightened off every person I thought might try to hurt you or prevent you winning the Tournament? I did. Who nudged Hagrid into showing you the dragons? I did. Who helped you see the only way you could beat the dragon? I did.”
- Harry Potter and the Goblet of Fire, Chapter 35 (Veritaserum)
The first thing he did after transfiguring Draco was check to see if he’d successfully hit Harry. His priority was making sure Harry remained intact.
“Moody turned to look at Harry – at least, his normal eye was looking at Harry; the other one was pointing into the back of his head. ‘Did he get you?’ Moody growled. His voice was low and gravelly.
‘No,’ said Harry, ‘missed.”
- Harry Potter and the Goblet of Fire, Chapter 13 (Mad-Eye Moody)
Barty Crouch Jr. would have likely held a grudge against Draco, since he’s the son of Lucius, a Death Eater who went free and didn’t use his freedom to seek out the Dark Lord. He probably saw an opportunity to have a bit of revenge on the son of a traitorous Death Eater, while still remaining in character as Moody. However, it’s equally important to note that Barty Crouch Jr. wouldn’t have acted on his hatred if it didn’t make sense (both as Moody and in furthering his own plot) since he never attacks Draco, Snape, or Karkaroff in any other situation. His main reason was almost certainly making sure Harry could still win the Triwizard Tournament.
“I told you, Harry … I told you. If there’s one thing I hate more than any other, it’s a Death Eater who walked free. They turned their backs on my master, when he needed them most. I expected him to punish them. I expected him to torture them. Tell me he hurt them, Harry …’ Moody’s face was suddenly lit with an insane smile.”
- Harry Potter and the Goblet of Fire, Chapter 35 (Veritaserum)
Moody turning Draco into a ferret would have also helped ingratiate himself to Harry, who he needed to earn the trust of so he’d be more willing to accept Triwizard Tournament help.
Barty Crouch was pretending to be Alastor Moody at this point in time. He's trying to act in such a way that people won't suspect that he isn't who he says he is.
This is why he teaches the students actual, applicable, skills, such as how to throw off the Imperious Curse. Him acting in a way that matches Moody's honorable character is part of that.
First off, it would be in character for Moody to respond like this.
‘I don’t like people who attack when their opponent’s back’s turned,’ growled Moody, as the ferret bounced higher and higher, squealing in pain. ‘Stinking, cowardly, scummy thing to do …’.
Goblet of Fire - Chapter 13: Mad-Eye Moody
Secondly, four Death Eaters vs two Aurors is a bit more of a fair fight than one student vs the turned back of another student.
We have heard the evidence against you. The four of you stand accused of capturing an Auror – Frank Longbottom – and subjecting him to the Cruciatus Curse, believing him to have knowledge of the present whereabouts of your exiled master, He Who Must Not Be Named –’
[...]
‘You are further accused,’ bellowed Mr Crouch, ‘of using the Cruciatus Curse on Frank Longbottom’s wife, when he would not give you information. You planned to restore He Who Must Not Be Named to power, and to resume the lives of violence you presumably led while he was strong. I now ask the jury –’
Goblet of Fire - Chapter 30: The Pensieve
It is unlikely that Barty Crouch Jr. thought (or cared if) attacking Harry was cowardly. It is also equally unlikely that he would be the sort of person to allow his previous actions to prevent him from casting judgment on someone else.
Ultimately, he needed to keep Harry alive and safe for Voldemort, and so in responding to the situation, he acted as Moody would have.
Because Barty Crouch Jr. is the type of person who will harshly judge others, but not himself.
While you could argue, he objected to Malfoy attacking Harry from behind as a cover for his disguise as Moody, I find this argument flimsy because he also immediately punished Malfoy by turning him into a ferret.
We know little of Moody's actual character, as we see very little of the actual person and not Crouch pretending to be him. We do know he was supposed to be paranoid to the point that others thought he was strange. However, he was never shown to have done such extremes when it had nothing to do with protecting himself or others, so I still question whether this was in character for Moody.
Crouch's act also drew the attention of McGonagall who said that is not how students are supposed to be punished. So, it in fact was arguably worse than if he had done nothing, as no one seemed to notice he was even there until he transfigured Malfoy.
Therefore, the ferret thing brought unwanted attention, and was possibly out of character for Moody. It makes me think Crouch did it without giving it much thought.
It is, however, completely in character for a Death Eater to judge others without judging themselves. How else could they justify to themselves the oppression, harm, and murder they committed against people whose only crime was not having "pure blood"?
