1) Chasing down flies 2) Chasing flies 
[baseball] In baseball, shagging is the act of catching fly balls in the outfield outside the context of an actual baseball game. This is most commonly done by pitchers during batting practice before a game, where they assist their hitting teammates by catching or picking up their batted baseballs and throwing them back to the pitching area...
• (p. pr. & vb. n.) of Shag
Picking up golf balls from practice ranges
To collect balls from a practice area.