Do you three-putt a few times during your round of golf? Are you the one who hopes your playing partner gives you that 3-footer? No such luck in a tournament. Try this exercise: place yourself on the green without any club (including the putter) and try to put the ball in a hole that is 25 feet away from you. Well, I guess you will face that hole and toss the ball underhand toward the hole. So why don't you putt that way?
Why don’t you put a 10 degree angle on the toe of the putter so when the shaft is at vertical position the toe of the putter would be flat on the green. Very simple answer “this is against the USGA rules.”
This is on the USGA website look at the picture (b) that would be non conforming using a putter that has 10 degree angle on the putter head if you try to putt with the shaft at vertical.
See at the figure 6(below).