Maria Elena Cruz watched the whole thing unfold shortly after 5 p.m.:

Just witnessed an assault on a woman at MGH Station. This amazing guy jumped out of his bike, in front of cars to save her. Huge dude choked and dragged woman to floor right outside the back-door exit of MGH. Guy riding bike on street jumps in front of cars to confront him. Woman ran away while hero was yelling at perpetrator. Police got there shortly after. Perpetrator handcuffed immediately.