If someone casts Hellish Rebuke on someone, does anyone in contact with the target catch on fire too?
You point your finger, and the creature that damaged you is momentarily surrounded by hellish flames. The creature must make a Dexterity saving throw. It takes 2d10 fire damage on a failed save, or half as much damage on a successful one. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d10 for each slot level above 1st.
There is nothing in the descriptions about contact other than “the creature that damaged you is momentarily surrounded by hellish flames.” That “surrounded” suggests a sort of area effect, but it doesn't specify anything about whether or not this spell does/does not spread through contact (that is to say, whether the "surrounding flames" also affect anyone within the radius or in direct contact with the target).
Best Answer
No.
The spell's mechanics are explicitly given: it deals damage to the foe that damaged you, with more damage in higher level spell slots and less on a save. Nothing in the text says it spreads through contact or has any other AOE aspect. The flames thing is merely a description of what the spell looks like.
Because 5e's designers hate everyone[citation needed], they have chosen to blend the flavor text in with the rules text rather than dividing them nicely the way 3.X and 4e generally did. A certain amount of confusion has ensued.