Using only the stylus, players acting as roadies must work to sabotage the rival guitarist's gear while repairing any damage done to the rocker they're supporting. Touching an arrow on the DS screen moves between Sabotage and Repair modes; it takes a few seconds, which factors into the fight.
On offense, players can sabotage their rival's amp, sound board, pyrotechnics, speakers and guitar. Messing up the amp, for instance, involves removing its back cover by unscrewing four screws, then unplugging the cables inside and reinserting them into the wrong sockets. To wreck a guitar, players first break the locks off its case, then snap its strings, re-string them backwards and use a robot arm to swap it out for the unsuspecting foe's. A ruined amp makes it hard for an opponent to see their notes, while a hacked guitar flips the notes; it's the most frustrating of the bunch.
The guitarist who's had these pranks pulled on them need to -- what else -- yell at their roadies to fix it. Repairing the damage seemed a lot easier than causing it. Fixing the pyros, for example, requires blowing on the screen to extinguish the flames. The guitar can be fixed simply by re-tuning it (rotating the stylus on its tuning knobs).
With all of the sabotaging and shouting, it's a ruckus, but still very, very fun. Who would have thought Guitar Hero would go and surprise us -- let alone the Wii version, which has up until now been a second-class citizen in the rhythm game mode.