You can have a chest with an enchanted crossbow (or any other item) that you clone to the position of the player and then you imidiately destroy the chest by using
/setblock in a chain command block.
Your setup may look like this:
The impulse command block clones the chest to the position of the player with this command:
/execute <target> ~ ~ ~ clone <chest coordinates> <chest coordinates> ~ ~ ~
And the chain command block will set the chest to air, while dropping the item(s) inside:
/execute <target> ~ ~ ~ setblock air 0 destroy
Note: Other players may be faster at picking up the item(s), they will simply drop to the floor near the player, they could also fall into lava, or get destroyed, or be lost in a different way.
Note 2: If the player is standing on a half slab, or inside of any block, then that block will be set to air, so it may potentially break parts of your map
* Line 1, Column 2 Missing '}' or object member name" as shown in the image, it is pretty much certainly the latest versions, as you can tell by the dark background of the GUI, I will add that information to the question. The information given is enough to answer the question though.