Shagging describes the act of catching fly balls in the outfield

Outfield

The outfield is a sporting term used in cricket and baseball to refer to the area of the field of play further from the batsman or batter than the infield...

 when not involved in actual baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

 games. Pitcher

Pitcher

In baseball, the pitcher is the player who throwsthe baseball from the pitcher's mound toward the catcher to begin each play, with the goal of retiring a batter, who attempts to either make contact with the pitched ball or draw a walk. In the numbering system used to record defensive plays, the...

s may do this during batting practice before games. In the Major League Baseball Home Run Derby

Home Run Derby

The Home Run Derby is an event played prior to the Major League Baseball All-Star Game. It is a contest among the top home run hitters in Major League Baseball to determine who can hit the most home runs. The event is currently sponsored by State Farm Insurance...

, children are recruited as shaggers in order to field balls that do not go out as a home run

Home run

In baseball, a home run is scored when the ball is hit in such a way that the batter is able to reach home safely in one play without any errors being committed by the defensive team in the process...

. Also, during batting practice anywhere, "shagging balls" describes the act of catching and gathering up balls that are thrown back to the pitching area, usually by a player standing near the pitcher.