Acts 18
12 When Gallio was proconsul of Achaia, the Jews with one accord rose up against Paul and brought him to the [c]judgment seat, 13 saying, “This fellow persuades men to worship God contrary to the law.”

14 And when Paul was about to open his mouth, Gallio said to the Jews, “If it were a matter of wrongdoing or wicked crimes, O Jews, there would be reason why I should bear with you. 15 But if it is a question of words and names and your own law, look to it yourselves; for I do not want to be a judge of such matters.” 16 And he drove them from the judgment seat. 17 Then [d]all the Greeks took Sosthenes, the ruler of the synagogue, and beat him before the judgment seat. But Gallio took no notice of these things.

I had to look up what was going on here because it doesn’t really say why Sosthenes was beaten. I was assuming I had missed something. Turns out, we don’t really know why he was beaten. However, Gallio watched an did not care.

Background info:

https://www.gotquestions.org/Sosthenes-in-the-Bible.html

After Paul had been in Corinth about 18 months, the Jews, led by Sosthenes, united in an attack on Paul, bringing him before the Roman proconsul, Gallio. As this city was under Roman rule, the Roman court was the ultimate authority in major disputes. The charge against Paul was that “this man . . . is persuading the people to worship God in ways contrary to the law” (Acts 18:13).

Gallio did not feel this particular issue was worth his time: “I will not be a judge of such things,” he said, and he ejected the Jews from the court (Acts 18:15). At that point, Sosthenes was seized and beaten as Gallio watched without interfering (verse 17). The text leaves it unclear as to who beat Sosthenes and why. Verse 17 simply says it was “the crowd there.” Paul D. Gardner, author of The New International Encyclopedia of Bible Characters, speculates that one of two things may have happened: 1) the Jews were angered that Sosthenes had been unable to persaude Gallio to try Paul and so made him the scapegoat; or 2) the Greeks outside the court beat Sosthenes because he was a Jew trying to stir up trouble in their city.