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Is it possible for the 17 year old to be charged with a criminal act of some kind? Yes, absolutely.
First, you have to be aware that it takes almost no evidence to charge someone. If someone testifies just to the actions you cover then it is possible for the boy that grabbed the girl's arm to be charged with assault/battery, some form of unlawful restraint, and potentially as a conspiracy to sexual assault since it could be argued that by preventing the other girl from going over and "helping" her friend then he made it easier for the sexual assault to continue.
It's harder to get a conviction since the burden of proof on that is very high, beyond a reasonable doubt, but it is still possible.
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