Princess Slay-Ya, Diva de los Muertos — you don't mess with roller-derby girls when they have names like that. A phenomenon that has become ubiquitous, women's roller derby has attracted a strong following in Kansas City, and for good reason: tough women athletes wearing tight shorts, cruising fast on roller skates. But men have also joined the elbow-throwing, ass-kicking, punishment-dishing party. The Cowtown Butchers are the first men's roller-derby team in town, and they take on the Indianapolis Race City Rebels at River Roll Skate Center (4720 Northwest Gateway, in Riverside, 816-587-0131) for Slamrock Showdown. The headlining match is preceded by a bout featuring rookie members of the Kansas City Roller Warriors, the national-award-winning women's league. The first match starts at 6 p.m., and tickets cost $10 for adults or $5 for kids. See cowtownbutchers.com or call 816-769-6040.