Eric Koston turned professional in 1991 when he joined the H-Street team. He went to live in the H-Street house in San Diego for six months. In 1992 Koston moved to Los Angeles when Natas Kaupas got him into the 101 team. On 101 he established himself as a leading switchstance skateboarder pioneering such technical tricks as the nollie flip noseslide and the switch kickflip backside tailside and also taking a switch 360 flip down the Embarcadero 7 during his part in 101's 1993 video Falling Down.

While many people believe either Koston or Karl Watson to be the inventor of the "crooked" grind, (nicknamed the K-grind after either Karl or Eric K), it was in fact Dan Peterka who invented this trick. Since the name Peterka is somewhat difficult to pronounce, and Koston was seen doing front-foot flips out of the grind a short time after its conception, the grind was renamed "k(oston)-grind" after his mastery of the trick. It was later changed to crooked grind as Koston was too modest to hold a title on a grind that he in fact did not invent.

In 1993 Rick Howard and Mike Carroll started Girl and asked Koston to join the team. He accepted and quickly became one of Girl's most influential skaters even creating his own trick, the Fandangle, which is a one-footed crooked grind.

Eric Koston was selected the "Skater of the Year" by Thrasher Magazine in 1996. He is one of the owners of a clothing company called Fourstar.

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