Holding :R2: when you're defending makes your player lock on your closest opponent.
If you aren't tackling and just moving with the D pad, holding :R2: where you want to stop will save your player from making a huge step towards the wrong direction, and keep him locking on the closest opponent while being aware of his surroundings. If the ball passes close to him he will perform the ideal interception of a pass. If you know Metroid or Zelda on the game cube you will know what it means to lock on an opponent.
If you are tackling with either :x: or :square:, well, you hold either button until your player reaches the opponent and what happens next? According to the new game, if you miss the ball you will colide with opponent and that makes it an ilegal tackle that you get punished for. The trick is to hold :R2: at the precise step you make before the impact and let go of the press button :x: or :square:. The reason I mentioned percision in timing the press of :R2: is because it reduces your speed. If you hold :R2: 2 steps before the tackle on 6 stars, a fast opponent will dribble past you.
As for the implementation, the best way to handle this tactic is to use the dual shoulder buttons the right way, which is one finger that shuffles between :R1: & :R2:.
Cheers!