3BU Ed Hickox made this call during the 4th inning of last night's Orioles vs. Red Sox game. It is an excellent example of Type B obstruction where a runner is obstructed in one direction, but is protected back instead. Hickox's mechanics are good too, first signalling the obstruction with a point, and then signalling the protected-to base with his other hand.
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http://menotomyjournal.com/mlbvids/obstruction.wmv