2 thoughts on “War Caster feat: Booming Blade as a reaction to enemy provoking at 5′ -> 10′, is a reach weapon valid for the melee weapon attack?”

1. What Jeremy neglected to explain, and is the key detail that clarifies the entire issue utterly is this: when you make an Opportunity Attack, the attack occurs BEFORE the enemy leaves the tile in question.

   If an enemy is 5 feet away, and it attempts to move to a tile which is 10 feet away, BEFORE it actually moves,you may make your Opportunity Attack. Since it hasn’t moved yet, it’s still only 5 feet away, and therefor Reach doesn’t matter.

   If your Opportunity Attack hits, then any applicable effects take hold.

   For example, if a character with the Sentinel feat hits a creature with their Opportunity Attack, that creature’s speed becomes 0 – which means it can no longer move. This occurs BEFORE it has left the square, so its Move is effectively interrupted and cancelled.

   Similarly, if a character uses War Caster to cast Booming Blade, and they hit with the melee attack, the spell’s effect takes hold BEFORE the target moves. At this point, the rules don’t actually dictate what happens, so the DM must decide. But it will either be that the creature automatically continues moving and automatically triggers the spell’s extra damage, or the DM may decide that the creature may choose to cancel their Move to avoid the triggered effect.

   Either way, you benefit. They either take the extra damage, or lose their ability to move – and both are valuable outcomes.

   Reply

   May 19, 2018 at 01:34

2. But moving from 5′ to 10′ when you’re wielding a reach weapon doesn’t trigger an opportunity attack (since your opponent isn’t leaving the area you threaten) which makes the original question moot.

   Reply

   October 25, 2020 at 00:24

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