Magic item, UA 100. Vague in its description. Use the following rules.
One missile can be caught per segment, per open hand.
No throw is required to catch a missile; catching is automatic.
For purposes of these gloves, a two-handed weapon can temporarily be held in one hand in order to catch a missile with the other hand, but only if the catcher is not attacking with their weapon on that segment.
If the missile is a thrown weapon OR if the catcher happens to have in their other hand an appropriate firearm (e.g. a bow when catching an arrow), the missile can be returned as an attack on the following segment. This does not count as the catcher's attack for the round.
If both hands are free and both hands catch a thrown weapon in a single segment, both weapons can be returned in this way on the following round.1)
If an arrow, bolt/quarrel, stone, or bullet is caught and no appropriate weapon is at hand for the return attack, the missile cannot be returned.2)
Missiles cannot be caught while casting a spell with a somatic or material component, or at any point prior to casting such a spell on a given round.