With a nod to the past and a wink to the future from behind their sunglasses, Baltimore’s The Dirty Grass Players have been pushing the leading edge of bluegrass music since 2015. As convincing on a 10-minute jam as they are on a 2-minute classic, they find an intersection between progress and tradition that in one set could inspire Flatt & Scruggs to reunite and then break up all over again.