Counterspelled Booming Blade

[Amnestic]

My table got caught in the trap of "if I let you do that, it undermines the feature of this other class", and I accepted the ruling because it seemed sensible, though it didn't sit right. It wasn't until it came up in a discussion on this forum that someone (Psyren, in fact) mentioned "well, that class gets to do it in this defined way, without a check, but that doesn't mean that others can't attempt to do something similar with some sort of check or roll" (I'm paraphrasing).

Now we just need to settle the argument of what Int (Arcana) DC I need to hit on my fifth level samurai fighter to cast Fireball.