The five-piece rock band O.A.R., from Rockville, Md., has a devoted national following -- selling out New York's Madison Square Garden twice, for starters -- even if it's lacked in mainstream recognition. The Washington Post's Chris Richards suggests the under-the-radar notoriety is on account of the band's non-buzzy roots-oriented sound: "easy, breezy, populist rock." It's definitely disarming, even charming, in today's pop landscape. Saturday, Aug. 13. Doors at 5:30 p.m. Merriweather Post Pavilion, 10475 Little Patuxent Parkway, Columbia, Md. Tickets are $35 to $45. Call 800-551-SEAT or visit merriweathermusic.com.