Edit: Do it on boring and kill second controller with flaming puck after slam dunk.
Will edit tommorrow fully.... Too tired.
The best way to do the 3 achievements for getting 25 medals is to triple up.
Start a match on minefield, bring the ball to the enemy base, and put your second controller at the edge of the goal and shoot it him. This is for Shot-Blocker.
Then bring the second controller that should still have the ball to the lower tight corner and check him with
this is for the Rough-Houser
Pick up the ball with your first controller and bring it to the goal. Killer your dummy with the spike and then slam dunk your ball while he's still dead for the Untouchable
The only downside to this is that there is a possibility of getting a Sir-Dies-Alot or a Sharpshooter medal in place of the ones you need.
The vast majority of the time you'll get 2 out of 3. A few times you'll get 3/3 and a few 1/3.
This is still far beneficial to doing each medal in their own games. As it only takes 10-20 seconds more and loading up each level takes a minute or so with load times.
Once you get one of the medals done you can take them out of rotation.
If you get Untouchable medal done early I reccomend switching to the "boring" map.