Ensure the opposition do not score any points in the match.
If you are having trouble with the 3 Legend diffculty achievements, you can easily get them all in a single Casual game.
Create 17 players covering each position (FB, 2x WING etc) in the Footy Factory with 0 attributes. This only takes max 15mins to do as you can quickly set the attributes to 0 by pressing the Y button. You need 4 subs for your created team to be valid.
Create a custom team then move/clone all 17 created players to that team through Team Management.
Once completed, start up a Casual match on Legend difficulty against your custom team. I used the Indigenous All-Stars but any team with 4+ skills in attack/defence will be fine.
You should have little trouble fending your way to the tryline nearly every set by holding RT to sprint and holding Up on the R-Stick to fend. Try not to pass the ball around too much to minimise the risk of a turnover, especially when in your half. When on defence, let your AI do the work and just stay behind the line incase they make a break.
Achievement should pop as soon as the match review screen appears.
Please comment below if I've missed anything or you are still having trouble.