Warning: Episode 2 spoilers ahead! The fifth season of Orange is the New Black began where Season 4 ended: with Daya pointing a gun at Humps, a guard who had been particularly vile to the inmates. She ended up shooting him in the leg, but her resolve wavered throughout the premiere. By the end of the first episode, Daya was making her way to Piscatella's office to call her mother after freaking out about what she'd done. But while she was picking up the phone, someone clocked Daya on the back of the head and took her gun. But who attacked Daya on Orange is the New Black?
It wasn't clear, at least not in the first few episodes. There was only one clue when it happened: a boot that looked like it belonged to an inmate stepping on top of the gun. But there could be one more hint, too: the weapon used to knock Daya out. It was the very same statuette Red had threatened Ginsberg with, which could point to Red as the attacker. She was the last person to leave the room (after Daya threatened to shoot her) and stealing the gun did seem like something Red would do; if she saw something that could increase her power, she would jump at the chance to take it. She was in the area, she had motive, and she wouldn't hesitate to take action. But is Red too obvious an answer?
The next time Red appeared on screen in Episode 2, she didn't give any indication that she might have the gun. She was happily wallpapering the halls of Litchfield with embarrassing pictures of Piscatella and not planning her next move with the gun, which one might expect of Red if she was really in possession of it. It looks like Red really could be too obvious a choice when it comes to who attacked Daya, unless the show is holding back for a major reveal that she is in possession of it.
It's possible that the gun was taken by someone who hasn't been seen for a while. Someone who is terrified of what's going on in the prison and is looking to find a way out — which they could do if they had a gun to prevent people from stopping them. This guess could be kind of out of left field, but I think it's possible that Judy King could have attacked Daya. After Soso left her alone in the library, Judy disappeared. She might have tried to sneak out, spotted Daya, and took the opportunity to get herself some protection. She was on the lookout for some, after all.
The show is playing coy about who attacked Daya and took the gun, which means the perpetrator is probably someone no one could see coming. When the reveal comes, it's sure to be shocking.