We ran into this reddit thread claiming the following:
A man fell onto the subway tracks in Boston, Massachusetts last night. Several passengers on the platform jumped down to rescue the man
More details as they emerge, but based on the video, this looks very courageous. The train light seems to indicate it's approaching rapidly. In any case, it is certainly a testament to the kind of community and quality of people in Boston. I really can't believe that guy crosses the tracks just to help out. Amazing.