The last part doesn't really make sense tbh. It would've been fine if she hurt her arm in the first place..the guy was already in cuffs. I guess they really wanted that dramatic effect :'D ...
At least it wasn't her classmates that got her arm broken though. With the way things were going I thought she was gonna get into an accident cause of them.
... That's not how police officers work, literally. Once they got the criminal arrested, the chance they let him pick up a weapon is absolute zero, left alone letting him run half a foot away from their guard zone.