Whenever I hear a man going on how he wants his gf or wife to lose in a fight, I await the "But sadly she won't fight for me. No idea why. " 
LOL well it depends on the woman technically, like guys, you have dominate and submissive women, women who like to lose and women who like to win, just like you have dominant men and submissive men, men who loves to be submissive (Such as the guys who likes to get beat up in mixed wrestling by women) and the men who likes to be dominant, (such as sexually dominate in bed) For example, I knew a few women in the fantasy cat fight industry and they actually like to lose because of the submissive nature of it. There's nothing wrong with either case, and to try and attack either side is wrong. But it definitely makes a lot of sense why both sides have their preference. I for example at a 6"3 male who can bench press close to 300 lbs, so I'm a naturally dominate person who prefer more submissive females. So for me personally, wrestling jobbers are some of the sexiest women on the planet, just because of their submissive nature.
I would agree that, generally, a dominant man is more likely to be turned on by the loser of a catfight than a submissive man would be. Though we are all individuals, of course, and there is no one rule which applies to every man.
The winner of the fight has proved herself to be stronger and more dominant than the loser, so a submissive man is likely to find her more attractive. Maybe she'll be strong and dominant enough to boss him around too?
Personally, I will usually know before a fight even starts which woman I find more attractive, and that won't change whether she wins or loses. So if my girlfriend got into a fight, which isn't likely to happen, unfortunately, and it wasn't a situation where I needed to worry about her safety, I would get a huge buzz from watching her, whatever the outcome, but probably more of a buzz if she lost.
The best way I could explain that is to say that I was brought up to view strength, aggression, and fighting prowess as "manly" virtues. So if a woman has those qualities, she seems less feminine to me.
I've found though, that if I get turned on by seeing a woman lose a fight, I will immediately start wanting to see her fight again, and win. As I said, there's no one rule that applies every time.
