Winning this achievement is more difficult than the description makes out. To get the achievement you need to start a (Become a Legend) match on the bench, then come on and help to improve your team's scoreline (ie equalise if behind or go in front if teams are level)... in ten different matches!
If you find that you're usually in your teams starting line up rather than on the bench then it might be at least two or three seasons before you can expect to unlock this one.
Having said that, some people (like Niebianski) have had it unlock after doing almost nothing, so there's no clear cut method for this one unfortunately!