What is that spell that sorcerers (I believe) use to spam-tag enemies?
The spell is kinda stormy (purple). It creates a round wave around the caster. Most of the casters used a staff and the animation shows it being pointed towards the sky.
I think one of the spell's morphs changes the spell to fire, but I might be wrong.
Best Answer
The skill you're looking for is Impulse
First take a look at the screenshot from the game:
This is from the Destruction staff skill line, which means that any class can use this spell. At the time of launch on PC this spell has been widely used on Dragonknights as Dunmers with a Flame staff equipped as this provided some nice passives for it.
Destruction staffs can be one of three types: Fire, frost and lightning. Depending on which you chose, the animation is colored differently (flames, ice ring, electricity) and the effects applied do also change for it.
I recommend you to use a flame staff for PvP, as this elemental type does more damage to Vampires, which are also common.
The morphs are Elemental Ring (adds damage over time) and Pulsar (reduces enemies' max health).
You can look it up on this wiki page if you need further information.
Below is a picture demonstrating the effect with an equipped Lightning staff:
Picture sources in order: deltiasgaming.com, nomadicgamer.files.wordpress.com