More than three weeks after counterprotesters attacked a pro-Palestinian encampment at the University of California, Los Angeles, the university police have made the first arrest related to the attack: an 18-year-old who officers said had beaten pro-Palestinian protesters with a wooden pole.

The U.C.L.A. police did not identify the man by name, but arrest records show that he is Edan On. He is facing one charge of felony assault with a deadly weapon. The police said he inflicted serious…