Baseball, like many sports, is a team sport that requires a lot of moving parts working in conjunction to execute a successful defensive play. This is especially true for infielders, who have to be constantly conditioned to making tough, accurate throws on the move. This requires muscle memory, developed through consistent practice. One way teams accomplish this is to "throw around the horn" following a strikeout.
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Around the Horn Drill
The basics of the maneuver begin with the catcher, who has caught the ball following the opposing batter striking out. In most cases, the catcher will throw to the third baseman, who will throw to the shortstop, who will throw to second baseman, who will throw to first baseman, who then throws back to the pitcher. The main reason for this drill is to encourage the infielders to stay alert following an out in which the ball isn't put into play.
The flow of a baseball game often involves short bursts of activity, followed by periods of non-activity. While the pitcher throws the ball to the plate, the infield is on edge, on its toes, waiting for the play. A strikeout cuts that tension immediately, and throwing around the horn allows the infield to stay loose and maintain timing.