This is one of those plays where you want to make the call for fear of penalizing B1 for being big. However, if he's big enough to not be put at a disadvantage by the contact, there's really no foul.
If it looks like the contact hurt him a good deal (a whole person flying into one's stomach can sometimes be rather painful), then you can call a foul. That's why we get paid to be judgmental; wait, I mean, we get paid to use our judgment.
