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He's got a pretty decent slider and slurve already, but his fastball is flat, his arm angle is low so it's easy to read fastball and get it elevated (no downward plane on his fastball) and he doesn't have a pitch he can use to get grounders when he needs them to limit damage.
Two ways to fix Olson...get him to think high in the slot and release the ball less 3/4 and more overand or develop a splitter or a 2-seamer or whatever you can that has straight-drop action.