How could you inflict financial or reputational harm on a shoe company? An empty threat.
Hold a press conference where he provides evidence that Nike was paying players in college, a la Adidas. FBI investigation follows. Stock price drops.
Very simple concept.
If you noticed, Nike has already suffered reputational harm in the last two months with one of their shoes blowing out on Zion's foot. Your premise that somehow shoe companies do not have reputations to maintain is ridiculous.