This is one of the less obvious parts of the game, yet has quite an impact on the performance of your players in a match, and the performance of opponents players too.
When you pick your team, you position you players on the pitch where you want them to play in the match, Goalie, Defence, Midfield, Attack and Left, Right, Centre, or any graduation in between. Opposing you are the opposition’s players and you can see their Talent ratings, Best positions and Injury status, exactly as you can see those attributes for your own players.
The key point is that players close to each other will mark each other and have impact on each other’s performance in the match. So if you put a strong defender close to a strong attacker it will tend to cancel his ability. Equally you can mark a player with more than one other. This works both ways though, the strength of your opposing players will affect players of yours that they are close too.
Finally a player in open space, unmarked will tend to play at full strength.
You can use this knowledge to set your team out. You have a choose of who and how to mark, and whether to go for space at the expense of marking others. Your choice!