「？」「！、」
"Is that some kind of uniform?" "Yep! I play field hockey."
Literal
Something [gen-の] uniform? / Yeah! I, field-hockey do-[am-ている] [because-から].
A quick Q&A. なにか + の + noun forms 'some kind of X' (literally 'noun of some [thing]'). The confirmer's response そ (for そう, 'that's right') is maximally contracted — spoken casual. あたし is the feminine casual first-person pronoun. フィールドホッケー is the loan for 'field hockey.' The trailing から gives the reason that justifies wearing the uniform. Very brief, natural female casual speech.