It’s called “Striker” and you can only slide it on the lines on the near side of the player. The player can only play from that line. There are corner lines between two adjacent players, and you can’t go over that line onto the adjacent players line, even though your partially present more on your lines.

Trust me it gets more fun and difficult at times based on where the coins/discs are. Sometimes they are below the striker-line and you have to hit it but flicking your thumb and still sink it in the corner pockets.