Jonah Lomu Rugby Challenge

First of all, in options - gameplay - make sure high tackle frequency is all the way to the right.

Start a local single play (two controllers one on each team) or online private match (make sure both players have high tackle frequency all the way up/right).

The two teams will be 1 good and 1 bad for ease only based on skill and time, I picked Australia vs Germany

Have the player gettng the achievement Australia, time 20 mins, pro.

Go into a ruck, have the Germany player win the ruck by pushing A or B. Once Germany has won/you regain control of the players he/she does not press LB or RB to pick up the ball, instead the Australian player will use this time to quickly run just behind the Germany player and high tackle (Y) him/her as they automatically pickup the ball. An offside will be given.

The Germany player will wait until the Australian player has picked one of two particular players (can be any players just use the same two each time). Line the player directly north of the Germany player and move an inch or two to the right. The Germany player hits B (tap) and not move. The Australian player will run directly south (as if you are going to run straight past him and not into him) and when you are beside hit Y and you'll do a clotheshanger type tackle rather then the standard, this is what your after.

Watch the first cutscene don't skip it, it'll show if he's getting a warning, yellow or red card (NOTE that if you are playing a local game you can press start and look at the players, it'll show anyone with a red or yellow card). It takes ten minutes for him to return after a yellow card.

Rinse and repeat.

NOTE that when the first half ends you can keep going for the red cards as long as the ball doesn't go off the field or you score. The achievement won't pop till the end of the game and Australia will need to win.

What I did to get both the red card achievements was:

2 player game (I used 2 controllers), pro difficulty, 40 min halves.
Lomu All Stars v Germany. Team wanting the achievement plays as Lomu All Stars.

I just scraped this. I got a straight red 10 seconds from full-time however I found a good technique that if I tried this again would take far less time.

Took almost 2 hours to find a rhythm. Let Germany win a ruck and get possession, I'd tap the buttons to add players for Germany to the ruck with the 2nd controller on my lap. Now, before Germany player takes the ball from the ruck (which they will eventually, you don't have to press B) go offside with a player from your side (Lomu AS) stand next to him and tackle him. Penalty. Then Germany have the chance to tap ball. (PRESS the button on the pad controlling Germany on your lap) This makes it clear to run with a Lomu AS player straight towards the German player holding the ball who has just tap kicked to himself. Then press Y when close to high tackle.

I couldn't find a solid tackling technique but late on I would get a lot of high tackle penalties against me if i ran almost around the player as opposed to directly at him with the ball and pressed Y. Would end up almost clotheslining them.

If you fail, just let Germany recycle the ball again from the resulting ruck, then do the same thing, go offside with a Lomu AS player, tackle the German player when he takes it out of the ruck, then wait until he tap kicks it and with a clear run charge at him and press Y.

Hope this helps.