Lil Herb and Earl Sweatshirt link up on "Knucklehead," an Earl produced track via Red Bull's 20Before15 Series. Earl and Herb spit effortlessly slick lines over Earl's soulful, lowkey production. The track is available as a free download to the first 1,000 fans here. 20before15 is a series of 20 exclusives tracks in 20 days from 33 artists who have been involved in Red Bull’s projects over the past year. Stream "Knucklehead" below and stay tuned for more from the 20before15 series.