Very easy to do, to earn Fundamentally Sound, you must Earn at least a bronze medal in all 5 Basic Offense drills inside of Skills Trainer.
In the skills trainer there are 5 bassic offense drills. In each one they task you with trying out the skill in a low risk practice session a few times and then moves on to the official challenge. You can either do these practice sessions and get the required level of correct actions or simply pause the game and select "skip" to advance to the actual drill. You will have 10 attempts in each of these drills.

The first drill is Pass Trajectory. You will have to alternate throwing lob passes by taping the pass button and throwing bullet passes by holding the pass button in the first drill. You must do the correct throw AND complete the pass for it to count. You will need 5 successful throws for a bronze. (7 for silver and 9 for gold)

Next is Acceleration Burst. Here you will have to use the RT button to sprint around defenders as a running back to get into the end zone for a touchdown. 5 successful actions will get you a bronze. (7 for silver and 9 for gold)

Field goal kicking is next. You will have to make field goals from various locations around the field. Line your shot up and hit the correct power to kick the ball between the goalposts. This is the easiest of the 5 drills. This one requires 6 for a bronze. (8 for silver and 9 for gold)


Punting the ball is the 4th drill. This starts out easy by making you punt the ball into wide areas or out of bounds after a distance. The last few kicks in this section however are quite difficult. You will be tasked with punting the ball to just a corner of the field or have the ball land in the final 10 yards of the field without going into the end zone. You will have to punt the ball in such a way that it lands BEFORE the zone you are targeting so that it will bounce towards your zone instead of landing it directly on the mark and having it bounce/roll away. 5 successes will get you a bronze. (7 for silver, 9 for gold)


The last drill is a 2 on 2 drill with you playing as the running back. All you have to do is get around a single defender to get the ball into the end zone. You can sprint around him with RT, spin out of his reach with B, stiff arm him with A, or whatever skill move you are comfortable with. The only requirement is that you reach the end zone. Once again you will need 5 successes for a bronze. (7 for silver, 9 for gold)

After the 5th drill is complete you will unlock the achievement and a Madden Ultimate Team pack as well containing 5 new cards/items to use in MUT mode.