Sashamorning
1,365,016 (801,115)
Achievement won on 16 Jul 14TA Score for this game: 2,038
Posted on 25 July 14 at 18:47, Edited on 30 July 14 at 22:17

This solution has 15 positive votes and 0 negative votes. Please log in to vote. 
Credit for this method goes to DigestedGolem, who posted the basics in the 23 star thread, and Zeh Marcoss who helped streamline the process.
If you're trying to boost this, you can definitely do it with as few as 3 players. It will take a while, of course, but it's a sure thing.
This must be done in the Online World Cup.
If you have alts, it'll be easier since it takes a lot of games. The good news is that one way or another, quitouts count.
Remember as you go through this to use teams that will let you earn these at the same time: and this will pop automatically:
You can also pick a team to help you win this one (just look for a team that has a terrible community average, since 3 opponent quitouts will net you a goal differential of +9, since forfeits count as 30 wins). It will pop after the Group Stage.
Here's the stepbystep:
At every step, make sure that Players A, B and C are the SAME LEVEL. Don't play 2.5 stars vs. 3 stars or 2 stars; they won't match as easily. When matching, make sure that both players change the search settings (3rd choice down) to Manual and search at the same time. It'll be obvious if you match. If you don't, remember that a 21 record will still pretty much guarantees a passthrough, so quit on your opponent and give them an easy win.
The basic idea is for the players to keep losing to A (by quitting), and then pushing each other up the ladder. It will take 14 games for each person to win the Cup once. Here's the process for all three to get their first Cups:
1) A over B. 2) A over C. C forfeits the tournament, restarting from the beginning at 00.
That's an important step.
3) B over A. A is into the Round of 16 at 21, B is 11 and C is 00. 4) B over C. B advances at 21, C is 01. 5) A over B (Round of 16). B is 00, C is 01. 6) C over B. C is 11, B forfeits the tournament, and is 00.
***Notice this pattern: every time the 2 teams in the group are at 11 and 01, the 01 team should forfeit to advance faster. It's a waste of time for a team to go to 2 losses.***
7) C over B. C advances at 21, B is 01. 8) A over C (Quarters). B is 01, C is 00. 9) B over C. B is 11, C forfeits the tournament, and is 00. 10) B over C. B advances (21), C is 01. 11) A over B (Semis). 12) C over B. C is 11, B forfeits the tournament, and is 00. 13) C over B. C advances, B is 01. 14) A wins the Cup. A is 00, B is 01, C is 00.
IF YOU ARE SOLO BOOSTING... you may want to switch to a different rated team to work toward another achievement. If so, all teams must be the same level, so reset everyone.
IF YOU ARE GROUP BOOSTING... follow these steps through, and when the third person gets it, begin at 1. If just boosting Cups for the 5x achievement, the person at 01 will be the next winner (B in this case).
B will now win the Cup.
15) B over A. 16) B over C. B advances, A is 01, C is 01. 17) C over A. C is 11, A forfeits the tournament, and is 00. 18) C over A. C advances, A is 01. 19) B over C (R of 16). 20) A over C. A is 11, C forfeits the tournament, and is 00. 21) A over C. A advances, C is 01. 22) B over A (Quarters). 23) C over A, A forfeits the tournament, and is 00. 24) C over A, C advances, A is 01. 25) B over C (Semis). 26) A over C. A is 11, C forfeits the tournament, and is 00. 27) A over C. A advances, C is 01. 28) B wins the Cup. A is 00, B is 00, C is 01.
C will now win the Cup.
29) C over B. A is 00, B is 01, C is 11. 30) C over A. C advances. 31) A over B. A is 11, B forfeits the tournament, and is 00. 32) A over B. A advances, B is 01. 33) C over A (R of 16). 34) B over A. B is 11. A forfeits the tournament, and is 00. 35) B over A. B advances, A is 01. 36) C over B (Quarters). 37) A over B. A is 11, B forfeits the tournament, and is 00. 38) A over B. A advances, B is 01. 39) C over A (Semis). 40) B over A. B is 11, A forfeits the tournament, and is 00. 41) B over A. B advances, A is 01. 42) C wins the Cup. A is 01, B is 00, C is 00.
Repeat these 14 steps to get the next person the Cup.
Good hunting! 