As long as we're on the subject, I had a DM prevent me from using a Rod of Absorption to negate a Counterspell recently. He insisted that Counterspell targets a spell and not the caster. I said that it says you attempt to interrupt a creature, which has a very specific meaning in D&D, casting a spell, which suggests you are targetting the caster and not the spell.
"You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect."
In any case I found a Crawford tweet saying that I was right, Counterspell targets a creature casting the spell and not the spell itself.
Yup. That's why you can't counterspell a caster under the effects of Greater Invisibility, or a sorcerer using Subtle spell - you can't see them casting the spell.
(I will admit that this seems a bit counter-intuitive to me - I feel like you should be targeting the spell and not the caster. It also makes for a better visual - seeing the spell rushing toward you only to be visibly disrupted by the Counterspell. It just doesn't work that way in 5e.
