Alice has Captain America as her ally. Bob kicks down the door and finds Crossbones:
If Captain America is in play when he enters combat, he gets +5. Then, Captain America must be discarded.
I ruled (since it was my game) that Cap must be discarded since allies are played from a player's hand to the table, so anything on the table is, "in play." My friends countered that the cards aren't in play because it's not Alice's turn and Alice isn't part of the combat.
I couldn't find a definitive ruling either way. Thoughts or suggestions?