Can Bone Skewer choose Ruin Runner from an opponent's hand to stun it?

Ruling: Yes, Bone Skewer can choose Ruin Runner from an opponent's hand. Ruin Runner's protection ability ("I can't be chosen by enemy spells and abilities") is only active while it is on the board, not while it is in hand.

Sequence:

• Bone Skewer is played and resolves
• A unit is chosen from the opponent's hand (Ruin Runner is a legal choice)
• When that unit is played, it enters stunned

Nuances:

• Passive abilities of permanents are typically only active while on the board
• Passive abilities that function outside the board are limited to cost alterations and rules that alter timing or how cards can be played
• Cards in hand are not permanents and their board-relevant passive abilities are inactive