to protect someone esle from the
attention or criticism due for a particular activity; To help someone in the performance of a task, but not directly assisting in the task.
From American
Football where certain players are detailed to prevent the opposing team from tackling the palyer with the
ball, by interfering with them.
a:"How am I gonna get these Playboys into the house while mom's there?"
b:"You go
round the kitchen
door, I'll run interference by showing her the job I did on the
lawn"