Credit for this goes to neeker75
Firstly, choose to control a weak team. Teams in the npower League 2, for example, are usually on one-star. Use any of them. Choose a strong team as your opponent - Manchester City, Barcelona, Liverpool - it doesn't matter.
Secondly, and very importantly, go to control settings and turn ''Auto-Switching'' to ''Manual''. By doing so, the game doesn't auto-switch you to a random player near the ball, which allows you to be in full control of the player you need to do the goal-line clearance.
Thirdly, switch difficulty to ''Legendary''.
Now, what you need to do is pretty simple. Once you win the ball, run back towards your goal and kick it out for a corner. When play resumes, quickly press to switch to a player near the goal, and have him run to the far post. With auto-switching turned off, the game doesn't switch you away, so you're safely tucked at the far post.
What happens next is all about luck. When the corner swings in, hope that the opponent connects with a header/shot etc. that flies past your goalkeeper and towards the far post. Press immediately to clear it if it does, and the achievement should unlock.
It may take a few attempts, but it's easier than waiting for a shot to come in (usually leading to a goal rather than a clearance because the opponents are just too quick), or trying to concede a freekick. Corners are easier to concede and if you fail with the clearance, you could concede another corner pretty quickly as well.