Why did she try to stop Brandon from kicking Derek's ass?

Remember, later in the movie when Brandon gets her the shotgun she says she can't use it, she's just not a violent person. That's probably why, seeing that right there was upsetting to her. Besides, alot of women are just like that, they just hate to see men fight or act violent, even if it is to stand up/defend them.

BTW, Tampa Bay unseated both the Yankees and Red Sox (or BoSox to you) in the AL East this season to reach their first playoffs, then defeated the Red Sox in the ALCS. But atleast they made the playoffs and got that far, the Yankees missed it, the first season since the wild card began in 1995 they'd failed to make the playoffs. That part probably made you happy, and although the ALCS result didn't, you (and all Red Sox) fans probably did feel somewhat happy for the Devil Rays anyway, they'd been so bad, and the doormat of pro baseball since their debut, then finally did good.

"I happen to be a vegetarian". Lex, from Jurrasic Park

Well, that's too bad, seeing as how Derek wound up killing Brandon!

I'm happiest...in the saddle.

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Because she's not an animal. She even says in the film, "I hate violence..I am not a violent person.."

"IMdB; where 14 year olds can act like jaded 40 year old critics...'

Some people will always try to stop a fight no matter the circumstances. Derek was certainly cruisin' for a bruisin'. It would have been an interesting plot twist if Brandon beat the living crap out of Derek then was arrested and charged with aggravated assault.