A Spectator (a lesser Beholder, described on Monster Manual p. 30) can use its reaction to use its Spell Reflection ability:
Spell Reflection. If the spectator makes a successful saving throw against a spell, or a spell attack misses it, the spectator can choose another creature (including the spellcaster) it can see within 30 feet of it. The spell targets the chosen creature instead of the spectator. If the spell forced a saving throw, the chosen creature makes its own save. If the spell was an attack, the attack roll is rerolled against the chosen creature.
My question is that if a ranger uses the spell Hail of Thorns and then hits the Spectator with an arrow, then if the Spectator makes its saving throw, can it redirect the thorns to another player?
The reason I question this is that the spell says that the thorns sprout from the ranged weapon or ammunition. In this sense, it seems that a person would have to have been hit by the arrow. However, other than this, the details of the Spell Reflection ability also suggest that it may be possible to make the thorns hit someone else even though it would still take the arrow damage.