Not being up on US law, I'll speak to what I know about Canadian law. Here, saying anything like "give us that tape or we'll sue" would constitute a threat, and that alone is a criminal act here. We have fairly severe fines and reasonable jail times for such behaviour. It is also entirely illegal for anyone to confiscate the personal property of someone else without a court order, or in the case of police, as part of the normal search and seizure after the subject has been arrested for criminal acts. And here, we also have stiff penalties for such unlawful confiscation of personal property, particularly if done under coercion (such as threatening a lawsuit).
It's as
O|||||||O said. The Nike officials had every right to tell them to stop filming, or eject them from the premises. If the people filming were ejected, they'd be trespassing if they entered again, whether or not they were filming. Oddly, some courts in some states have set such a crime as precedent to be used as a tort to convict the same person of photography on a premises that they've been banned from. Really weird.
Anyway, what the Nike officials did was criminal. And in Canada it would be criminal regardless of whether or not the property was given willingly (because the people giving up the property could be considered to be in distress). I'm reasonably sure it works similarly under US law.
Confiscating the property is beyond their rights (and even beyond the rights of a police officer if they weren't doing anything criminal). Ejecting them from the premises for not following the reasonable rules they put in place is not.
What I think is most unfortunate about this situation is that this will set a precedent in many people's minds, particularly people of some authority over a particular premises (say, a store, or restaurant, or what-have-you), that they can freely confiscate cinematographic or photographic media from anyone on their turf. (I'm just thankful I've never had to explain this to anyone. I've been asked to stop taking photos in stores before, or even just asked if I was taking my photos for profit—in which case I just kindly explain what I'm doing, and put away the camera or make nice and keep shooting.)