The immigration rebel: 21 Savage closed his set with a massive rap-along moment, the 4 million-selling single “Bank Account,” which had the audience punctuating every syllable of its countdown refrain with a fist punching toward the stage. Part of the enthusiasm no doubt had to do with affirmation. 21 Savage, who is a citizen of the United Kingdom, was arrested earlier this year by U.S. immigration authorities for allegedly overstaying his visa. But his court hearing has been delayed and for the moment he’s free to ply his trade as one of the most commercially successful rappers of recent years. His set drew one of the largest audiences of the festival, eclipsing the numbers that gathered for the Strokes’ headlining set Thursday. It was a stark reminder that this isn’t yesterday’s Lollapalooza anymore. In this world, hip-hop and pop are ascendant and 21 Savage is a star while the Strokes, with their last studio album out in 2013, are elder statesmen from a bygone era when rock was still the primary musical language of youth. (Greg Kot)