The Ring Spark Field is an attack used by Metal Sonic. When using this move, Metal Sonic unleashes a powerful electric field around him at the cost of lowering his speed.
When using the Ring Spark Field, Metal Sonic uses an internal radioactive force within him to create a powerful electrical discharging field around his body to damage anyone that comes too close to him, and has enough power to tear metal foundations apart. The downside to the Ring Spark Field, however, is that Metal Sonic has to rerouted so much of his energy output from his other systems into the attack that his mobility deceases considerably and leaves him worn down for a few moments.
Sonic the Hedgehog CD
The Ring Spark Field first appeared in Sonic the Hedgehog CD during Metal Sonic's race with Sonic on Stardust Speedway. In this game, whenever Sonic comes close to Metal Sonic while he is moving along the ground, Metal Sonic unleashes his Ring Spark Field to halt Sonic's advances. When performing the Ring Spark Field in this game, Metal Sonic flashes red while releasing blue electrical charges, but the attack's range is very limited.
The move returned in Sonic Generations during the game's recreation of Metal Sonic and Classic Sonic's fight on Stardust Speedway. In this game, the Ring Spark Field looks completely different, is colored yellow, and has a much further range than in Sonic CD. Unlike in Sonic CD, however, Metal Sonic uses the Ring Spark Field in the air rather that on the ground, but can send two columns of electricity from the bottom of the electrical field, down to the road where Classic Sonic is running, thus limiting the space he can run on. When Metal Sonic is about to use the Ring Spark Field, he charges up the attack, which is signified by a pulsating electrical field surrounding him, before finally attacking.
In Sonic Generations, Metal Sonic is vulnerable while charging the Ring Spark Field.
In Archie Comics this ability is called "Burst Shield".
↑"Created by Dr. Eggman and programmed to destroy Sonic, Metal Sonic is a robotic copy of our hero and shares many of his abilities. He can mimic Sonic's spin dash and homing attack, and thanks to the jet engine in his torso he can beat Sonic's acceleration and equal Sonic's speed! He has extra abilities however, due to his mechanoid form. These include his Ring Spark Field, telescopic limbs and a forcefield known as the Black Shield" - Metal Sonic's biography in Sonic & Sega All-Stars Racing.