COMMON If you fight a rearguard action, you try hard to stop something happening when there is little possibility that you will succeed. Groups, both on the left and the right, are still fighting a rearguard action against the plan. Note: Other verbs are sometimes used instead of fight, such as mount and stage. The opposition party have mounted a desperate, rearguard action against economic reforms. Note: You can also just talk about a rearguard action. However, the rearguard action may prove too late. Note: The rearguard of a retreating army is a unit which separates from the rest and acts as a defence while the rest of the army is getting away.