Interdictions happen when a enemy ship pulls your ship out off supercruise whilst travelling in a system. This will result in a small tug of war mini game where you have to keep your ship lined up with a escape vector in the form of a blue circle that will move around the screen and even out of view if your to far away from it. If keep your ship lined up a blue bar will fill up on the left side of the circle, when it’s full your ship will escape interdiction. Alternatively if your can’t keep your ship lined up a red bar will fill on the right of the circle, when this fills you will be dragged out of supercruise by the enemy. After 50 successfull escapes you will get this Achievement.
Carrying valuable cargo will help you to get chances of being interdicted, as will having a bounty on your head.
It’s really not that hard to escape interdictions but will take some time to get 50 for this Achievement, plus there is a follow on Achievement for getting 100 successful escapes.
Good luck with the Achievement.