NFL QB Trevone Boykin is in custody after being arrested Wednesday for allegedly punching his girlfriend and cracking her jaw ... TMZ Sports has learned.
Boykin was being investigated by cops in Mansfield, Texas after he was allegedly involved in an altercation with his longtime GF Shabrika Bailey last Wednesday.
TB -- who was cut by the Seahawks on Tuesday -- vehemently denied any involvement in a physical fight with Bailey.
However, Bailey -- in an interview -- told a different story, claiming Boykin choked her and broke her jaw before finally taking her to the hospital for treatment.