The wizard is chased through the woods by a bandit. The bandit is 50 feet behind the wizard and continuously throws javelins at him. The wizard then readies a Catapult spell. The trigger is "after the bandit releases the next javelin". Of course, the bandit throws another javelin.
Now comes the strange part… do I really have to roll for the bandit’s attack? Because it seems to me, that no matter if the bandit would hit or miss, the Catapult spell will pluck the javelin from the air and hurl it right back at the bandit.
The trigger is perceivable. The reaction (casting the Catapult spell) occurs after the trigger (but before the javelin hits?). And the javelin seems to be a valid target for the Catapult spell: its weight is between 1 and 5 pounds, and at the moment when the spell is actually cast, it is neither worn, nor carried.
My players like it, I'm not a fan.
Does this work with RAW? Is this an intended use of the Catapult spell?
Best Answer
The contentious part of this question is the trigger for the Readied Action
The relevant rule for setting the trigger for a Readied Action is as follows:
Xanathar's Guide to Everything elaborates further:
So, does 'when the bandit throws a javelin, but before the javelin hits' work as a trigger?
It's not really clear, RAW.
It could be argued that, if someone sets this trigger as 'when the bandit throws a javelin' then the trigger is finished or completes as soon it leaves the bandit's hand, in which case the Readied Action will interrupt the bandit's Action and potential damage from it will be avoided before the roll is resolved, to know whether it would have hit or not.
However, it could also be argued, that the trigger completing or finishing in this case means the bandit's Attack completing or finishing (i.e. both hit and potential damage being resolved) before the reaction is triggered. Ruling this way would make readying the Catapult spell basically useless, as Casting Catapult on your next turn and keeping your reaction free would always be more efficient.
Which way you rule on this is up to you.
I personally, would want to reward creative thinking, and so would rule as follows in my own game:
It works, for the reasons you've stated:
And I'd allow it, because I don't think doing so is overpowered:
In most situations Shield (also a first level spell) would be a better solution:
P.S. An interesting aside, that hasn't been covered by this answer or any other, is that Catapult would probably break the javelin it was cast upon. Catapult deals 3d8 damage not only to whoever it hits, but also to the projectile itself. So, a DM would have to rule on how many hp a javelin had, but Catapult-ing it would almost certainly break it (for comparison, a Chain has 10 hp, a Rope only 2 hp).
This would prevent the same javelin being thrown back and forth, and mean that a pursuer would eventually run out of javelins in this situation - despite the fact that they are being 'returned to sender'. Whether a broken javelin could then be thrown as an improvised weapon is up to the DM (though it would still be a lesser damage die than an unbroken javelin, and have a smaller range).