This is exactly how late Brackstone was. About a foot and a half.
The ball was travelling directly away from Brackstone but it was not travelling towards their player, who had to cut across to intercept it. In doing so he ran into the path of an oncoming train.
The only way out for Brackstone was to have given up the chase earlier, though I don't really see why he should as it was his ball. Going at full pelt there wasn't much he could do to avoid the Boston man.
But he did not make a lunge for him. He caught his trailing leg as you can see from the moment of impact.
The referee and linesmen, of course, did not have the advantage of slow motion. That's football.