I've been playing Ride to Ruin's action as requiring a Rohan Ally in play in order to be discarded and pay the action's cost, but I was wondering if this is an inaccurate or at least overly limited interpretation: could I discard a Rohan Ally from my hand to fulfill the condition of the card's action? Thanks.

no, i would say you have to have it in play to discard it, im sure it would say 'from your hand' otherwise

Rather than offering a long and superfluous explanation, I will stick with 'What richsabre said.'

WarrenLocke said:

The answer is NO, but it is not a silly question.. it is again, one of the problems with this game having loose terminology. There are 3 compleatly seperate keywords for entering the discard pile, and no keyword for entering it from the hand. Most games use "discard" to indicate placing a card from your hand into the yard. But as I said , discard is one of three keywords that mean the same thing, for now at least, having the three keywords means that in future cards they could make effects that trigger off these slightly diffrent meanings.. but for now they are exactly the same meaning... and that meaning is "entering the discard pile from IN PLAY"

This is why protector of Protector of Lorien has the qualifying text "from your hand" printed on it. So unless you see "from your hand" it means "discard FROM PLAY"