Counterspelled Booming Blade

[Theodoxus]

Depends on the interpretation: "As part of the action used to cast this spell, you must make a melee attack..." vs "You brandish the weapon used in the spell's casting and make a melee attack..."

That word 'Must' in the SCAG version makes it imperative that the attack has to happen, and disrupting the attack (either via CS or something like Parry), negates the spell and the attack.

Tasha's changed the wording, making it a bit more ambiguous; does the attack happen prior to the spell? Plain English reading it appears to be so. The description continues "On a hit, the target suffers the weapon attacks normal effects, AND THEN becomes sheathed in booming energy..."

Given the discussion at the start of the thread, as well as various anecdotal evidence (including a couple DMs I play with), the answers run the gamut of no effect at all to melee weapon still hits and deals damage, just the booming portion is negated. If folks can't agree on the interaction, it must needs be RAW needs refinement in this matter. Given that the SCAGtrips appeared after the PHB was written, AND Tasha's more ambiguous rewording long after, with no (as far as I've been able to determine) errata directed expressly at the interaction between CS and weaponized spell attacks... I stand by my sentiment on the interaction between the two.

I have an even easier one - reject the idea that anything needs 'fixing' about this interaction and keep playing as normal.

This reads as "just play it like your DM told you to and don't come crying asking around here what we think. I'm sure I'm wrong, and that's not what you meant.