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"