Instructions
Score a goal on offense, but don't skip the celebration. To do this, don't press any buttons after scoring a goal for a few seconds.
Press "X" on the Xbox 360 or the square button on the PS3 to switch players after scoring the goal to pick your goalie.
Hold down the left trigger and twirl the right analog stick in a clockwise motion starting from the top. This should execute a cartwheel, which can be done by any character on the team that scores a goal, and not just the goalie.