Road warriors with a work ethic to rival that of the Dead, the Roots are best witnessed live. The members of this Philly crew form a jam band in the best sense: They play off each other like beboppers, and you haven’t really heard them until you’ve seen them. Opener Jeru the Damaja doesn’t spread old-school aesthetics with the faith-driven verve of the headliners, though he practices what they preach. Jeru’s latest, Wrath of the Math, is a spare affair, infused with his sober, staccato flow and the steady swerve of Gang Starr’s DJ Premier. At 7:30 p.m. at the 9:30 Club, 815 V St. NW. $18. (202) 393-0930. (Brett Anderson)