if you are struggling with this (like I was - getting to about 63% trying it normally!)
Go to exhibition mode.
Choose a really good side and a poor side.
Choose Beginner difficulty.
Score as many goals as you like, maybe working towards the score 100 goals / 50 assists achievements too.
Pass the ball amongst your defence as much as you want, even passing back to your keeper to hang onto the ball as long as possible before passing it to a teammate before you get tackled!
You can keep an eye on your possession percentage by pressing pause at any point in the match.
The achievement will ping at the end of the match.