Complex sentence: Opposition leader Sergei Udaltsov, who was protesting in support of the band, was detained by police, while former world chess champion and a long standing opposition member Garry Kasparov, trying to attend the reading of the verdict, was arrested and beaten.
Split into simpler sentences: Opposition leader Sergei Udaltsov, who was protesting in support of the band, was detained by police. Former world chess champion and long standing opposition member Garry Kasparov, who tried to attend the reading of the verdict, was arrested and beaten.