leadership would be a proficient word alone.
This does not seem right. Proficisnt means skillful. Maybe you mean "adequate."
y natural leadership ability really worked well for me when---- this sounds like bragging. Maybe you should give an insight you gained about leadership -- something about encouraging others, perhaps -- instead of just claiming to have natural leadership ability.
My offense lined up in formation as I stood tall behind the center and gazed out at the defense.---- yes, all of this sounds very pompous! I'm sorry, I know you don't intend it to seem that way.
I suggest writing something that expresses humble appreciation for the role you got to play as a leader, despite your young age, etc., and then make a connection between leadership and your chosen field of study.
:-)