This achievement requires you to win the Ones Eliminator Tournament, which is in the World of Chel section of the game. It is 100% online. You need to win 4 consecutive rounds of ones, which 1vs1vs1. Your online opponents are also on your same round, meaning in theory your opponents get more difficult per round as they have also won.
I'm writing this as I have just unlocked this, and as an average at best NHL player I want to say it is doable for everyone out there. It is a high skill achievement, so practice practice practice. Good players shouldn't have too much trouble. I wanted to give some quick tips and techniques I came up with:
-Learn where the puck is going to go. The goalie is consistent to where he releases the puck. If he's facing the left wall, and on that side, he will dump it over there. Same on the other side. If people are on top of the goalie, head over to the back and wait for a spawn. Puck possession is key especially in the higher rounds.
-I used two ways of scoring the entire time. If I got a breakaway, I would do a simple backhand to forehand move, or forehand to backhand. Use whatever you are comfortable with on a breakaway. Learning how to be somewhat accurate from mid range wrist shots is vital.
-Judge your competition's styles. If they are overaggressive going for hits and stuff, skate around them for easy breakaways. This is more common in the early rounds. In higher rounds with more skilled, and cautious players, they tend to camp the net and play lock down defense. This is when puck possession is key. Skate around and either capitalize on a mistake and get to the net, or snipe the corners from a distance when you have a lane.
-Most importantly, know what not to do! Don't take slapshots. If you are taking a wrist shot, make sure it's going in or not hitting the net at all. Dumb shots = easy rebounds for an opponent. Be VERY careful when hitting people, as half the time it gives the third person a clean break. (If someone in your game is hitting people, be that third person). I only hit someone when they were smaller, and I was one on one with the person.
-For your build, I HIGHLY recommend using someone big. I had the most success with a Power Forward. I was 6 foot 7, 247 Pounds. Definitely use Brute Strength 2. Quick Wrister 2 or Offensive Minded 2 are good choices for the second spot. I used drive the net for the specialty. Being big is key or else people will hit you constantly. Very rarely do you need the extra speed.
-Know the score. If you're down 2-1-1, with time expiring. Work together with the other person at 1 to tie the game to keep it going into OT. Better to need to score 2 unanswered in OT than just lose at the end of regulation trying to be selfish.
-Don't give up!! I lost in the finals 8 times, 6 times by one goal. It can be frustrating if you aren't good at NHL, but it is possible!!