I realize a hard thump to the chest could do that, I just don't feel like that is what happened at all. Tough to speculate from a short video, however. When you make a tackle, you brace yourself for the impact. For a thump to do that, I would imagine it would have to be a scenario in which the impact was greater than the player expected or he was unable to protect the area. If this were the case, I would presume that we would have seen at the very least multiple tackles result in similar issues in our lifetime. Of all the tackles made and all the players that get tackled over the course of a season & multiply that times 45. That is just in the NFL. Add college to that...what are the odds really?