I'm pretty late to the party here, so I'll probably say stuff that has already been said....however, I do not for the life of me understand why an employer (really any employer but especially an employer of people in a union) think for the life of them "cooperation" in an investigation means they get to completely invade your privacy.
To me "cooperation" means they ask you questions, and you answer them. They want to see the footballs so you give them to them. But take cell phones from 5 people? Who the heck do they think they are, the NSA? Even the NSA isn't supposed to do that.
If I'm the NFLPA I'm standing united on this and saying the following:
"All our players at any and all times are always in complete control of their phones, their email and social media passwords and logins, their diaries, their trash, their homes, their photo albums, their cars, their academic records, their yards, and any other similar part of their private lives and the NFL can never have access to them ever. Our players will comply with warrants by law enforcement, but not ever the NFL. This is non-negotiable. It doesn't matter if they burn them, send them to the moon, smash them with hammers, or delete it. It is their property."
Go on strike if you must, but win this battle.
The end.
I don't recognize an employer's right to your stuff. They have a right to their stuff.