Win a match of Mouse Polo by 15 points or more.
This achievement can be earned in the Mouse Polo mini-game in story mode, or you can select the mini-game directly (by clicking on the mouse symbol in the level-selection screen) after finishing the second story level, The Polo Lounge. This achievement requires that you win a game of Mouse Polo by 15 or more points. This could take a few tries, but once you get the hang of the game, it is not too bad. First off, you will want to play the Flower Power-up mini-game (pick from level-select screen) beforehand to get up to four points added to your score before the game. When you select the Flower Power-Up mini-game, you will be immediately prompted with choosing which other mini-game you want to apply your boost towards when you win. Choose Mouse Polo and attempt to earn as many points as possible by avoiding pollen to rack up big multipliers. If you score 1000, 2000, 4500, and 10000 points, you will earn 1, 2, 3, or 4 automatic points to start your Mouse Polo game. Immediately go play Mouse Polo after finishing.
The key here is to be quick and go for the throat. Remember that your teammate can also score and to run picks for them if they have the acorn (i.e. block the opponents for them). Be sure to collect power-ups if you see any. Some of them are essentially automatic goals. Avoid the mud as it will slow you down. There are three 90 second rounds. At the end of the third round, you must be up by 15 or more. This is probably the most challenging achievement in the game, but with a little practice, you will have this in no time.