From Rampage Knights Wiki
How to beat the challengeenemies including Orcs, Skeletons, Knights, Demons and Goblins may carry shields. Shields can be damaged using a Jump Attack (jump up and press the attack button in the air) or Dash Attack (hold attack button then press left or right). Some shields will be destroyed in a single hit, whilst others take two hits.
Dash attacking large groups of enemies is an effective way of destroying large numbers of shields quickly.
Breaking shields does damage and creates a shockwave.