The Angel Ring is Pit's Side Special Move in Super Smash Bros. Brawl. He rapidly spins his bow in front of him and damages opponents, as well as deflects incoming projectiles, Thus making this an ideal move to use against characters such as Snake. This move was replaced by the Upperdash Arm in Wii U/3DS.
It's worth noting by using Angel Ring in midair, Pit can move slightly in the direction he is facing. Also, Pit cannot fall off ledges when using this attack.
This is the only one of Pit's Special Moves not based on one of the Three Sacred Treasures from Kid Icarus. In fact, Pit could not use any sort of move like this prior to Super Smash Bros. Brawl, as his bow did not double as a pair of blades. However, it could be based on the Projective Crystal, a circulating barrier item found in Sacred Training Chambers in his game. The item creates two circulating crystals, which would protect Pit from incoming enemies in a similar fashion.