Meanings
From cricket, where hitting the ball over the boundary without it bouncing scores six runs, the maximum for one shot.
How to pronounce "hit someone for six":
AU
To score six points against (a bowler) by hitting the ball over the boundary.
To affect in a devastating way by some unexpected news.
Example: "When I heard about the accident, it hit me for six."
To hit another person very hard.
Example: "When he swore at me again, I couldn't hold back. So, I hit him for six."