If my opponent plays stand your ground can I respond with an iron discipline and target the unit in the discard pile to negate the effect?

FAQ 2.2 page 11 states:

"Unless otherwise stated, a card can only target cards that are in play."

Iron Discipline does not otherwise state it can target out of play cards (out of play is the deck, hand, and discard pile).

So I would rule that you CANNOT target the unit in the discard pile.

Got it. Thanks