My wife was reading this over my shoulder and said all those people claiming this is gross or unrealistic for a 15-year-old girl, who's probably been interested in boys since she was twelve, getting turned on by a boy defending her don't have the slightest clue what it's like to be a teenaged girl.
You know, when I was in junior high school, drama girls and mean girls CONSTANTLY started 'let's you and him fight' crap between guys BECAUSE they get turned on by the drama. I still have a big scar under my left eye from a fight when I was fourteen caused specifically by a girl trying to get some dramatic action, and that was a fight I WON.
As far as ACTUAL sex, yeah, technically it's illegal to describe anything like that in this country until they are eighteen years old (when I was growing up it was 16, but I guess Millennials act like preschoolers until they are thirty now.) but teenagers being teenagers? just be careful to draw the line at 'prurient interests' (No describing them playing with themselves even though EVERYONE knows they do it)
Considering the amount of smut on SH, I am actually surprised at how many pearl-clutching Puritans there are in the forums here. I started having sex when I was fourteen, and that was a LATE age to have a girlfriend.