[RPG] How does line of sight for spells work, accounting for familiars


I had to make a call today and I'm wondering how this scenario should've gone down

The map was a U-shaped hallway; the party was on the lower left of the U, with the enemies on the upper right. The wizard has an owl familiar who could see an enemy caster, with the wizard seeing through the familiar's eyes, and the wizard was further back.

The enemy caster cast a fireball.

The player claims that since he was looking through the owl's eyes from his turn, he should technically have line of sight for a counterspell.

Could counterspell be cast in this case, even though there was a wall between him and the caster, and he was physically not able to cast towards the enemy caster?

Was I wrong in said judgement?

Best Answer

You cannot cast the spell because spells require a clear path to their target

The counterspell spell requires us to see the target as it states:

1 reaction which you take when you see a creature within 60 feet of you casting a spell

And we can do this but the more general rule on spells from the "Targets" section states:

To target something, you must have a clear path to it, so it can't be behind total cover.

However in this case we do not have a clear, unobstructed path to the target and so we cannot use counterspell in this way.

This is also supported in the following questions: "Is it legal to cast a spell with a range of Sight on someone you can see, but without a clear path?" and "How does line of effect work with spells targeted through the Sentinel Raven's sight, from the UA Raven Queen warlock patron?"

Familiars only help to extend the range for spells where the target is yourself and which require you to have line of sight such as misty step as gone over in this question: "Can a wizard use his familiar's senses to enlarge his “you can see” area?" or to extend the range of touch range spells as gone over in this question: "Does a touch-range spell cast using Find Familiar have to have line of sight from the caster?