GO:0033842:   N-acetyl-beta-glucosaminyl-glycoprotein 4-beta-N-acetylgalactosaminyltransferase activity
Catalysis of the reaction: UDP-N-acetyl-D-galactosamine + N-acetyl-beta-D-glucosaminyl group = UDP + N-acetyl-beta-D-galactosaminyl-(1->4)-N-acetyl-beta-D-glucosaminyl group.