Prosecutors say 30-year-old Herbert Alex Simpson, of Philadelphia, pleaded guilty to two counts of mailing threatening communications.
Simpson sent Coughlin letters threatening to expose a fictitious sexual tryst with two women.
Court papers initially filed by prosecutors said the letters demanded the coach pay $20,000 to $30,000, but defense lawyer Nialena Caravasos notes that the charges of extortion were dropped.
She says her client has disabilities that require a mental health exam and that will be taken into account at his sentencing, which is scheduled for Feb. 26.
Simpson faces up to 10 years in prison, a $500,000 fine, 2 years of supervised release, and a $200 special assessment.