The latest Unearthed Arcana includes a spell Flame Stride:
The billowing flames of a dragon cover your feet, granting you explosive speed. For the duration, your speed increases by 20 feet and moving doesn’t provoke opportunity attacks.
When you move within 5 feet of a creature or object that isn’t being worn or carried, it takes 1d6 fire damage from your trail of heat. A creature or object can take this damage only once during a turn.
The spell specifies when you move, so a creature approaching you would not take the damage. but what if the character was hit by a Thunderwave spell and knocked back 10 feet, would any creatures the character passes or finishes movement next too still take the flame stride damage?