With riots breaking out across the U.K., some are wondering if the unrest could spread to America. Already in the past few months, youth mobs have wreaked havoc in Philadelphia, Milwaukee and Cleveland. "The age range is interesting — of most of these riots, it tends to be in the teenage to early 20s by and large," said Frank Farley, a professor in the College of Education at Temple. "That's a big age for thrill-seeking and risk-taking."