A more thorough explanation:

Mahanoy Area School District v. B.L. is a 2021 U.S. Supreme Court case that dealt with whether public school officials can regulate student speech that occurs off campus. The case involved B.L., a student at Mahanoy Area High School, who posted two photos on Snapchat over the weekend. One photo showed B.L. and her friend with their middle fingers out and a vulgar caption, while the other expressed frustration that she did not make the varsity cheerleading team. One of B.L.’s Snapchat friends shared these photos with others, and eventually, the photos were revealed to a cheerleading squad coach at the school. In response, school officials suspended B.L. from the junior varsity cheerleading squad for the upcoming year. B.L. filed a lawsuit, arguing that her First Amendment rights had been violated.

The Supreme Court ultimately ruled in favor of B.L., stating that the school could not discipline her for her off-campus speech. The Court outlined three categories of speech that schools can regulate: 1) “indecent,” “lewd,” or “vulgar” speech on school grounds, 2) speech that promotes illegal drug use during class trips, and 3) speech that appears to “bear[s] the imprimatur of the school,” such as a school newspaper. However, the Court also recognized that public schools may be justified in regulating off-campus speech in particular circumstances.

The Court found that B.L.’s speech was protected by the First Amendment because it occurred outside of school hours at an off-campus location, with a circle of her friends, and did not identify anyone specifically in her posts. The Court also found that the school’s interest in prohibiting vulgar language in criticism of school officials was diminished in this case because B.L. did not use vulgar language on school grounds, and the school was not acting in loco parentis.

Justice Alito wrote a concurring opinion, providing a framework that courts might follow when analyzing a case like this. That opinion suggests the question courts must ask in cases like this is whether the parent can be reasonably understood to have given the school the authority to regulate the student speech in question. Justice Alito also advised courts to take notice of the difference between vulgar speech that targets the school and vulgar speech that targets a particular individual of the school.

Justice Thomas wrote a dissenting opinion, where he stated the majority opinion was ignoring historical cases that found schools can regulate speech that occurs off campus when it has a proximate tendency to harm the school, students, programs, or faculty members.