"A goal is scored ONLY if an attacking player strikes the balls with the end of his/her mallet, and the ball crosses the goal line between the goal posts. If the ball is hit with the flat side of the mallet and crosses the goal line, the shot will be called a "shuffle" and the play will continue." http://www.polo-velo.net/english/rules/reglesaxlesofevil.htm
I know, I know, it doesn't answer your question. It's all I could find.
"A goal is scored ONLY if an attacking player strikes the balls with the end of his/her mallet, and the ball crosses the goal line between the goal posts. If the ball is hit with the flat side of the mallet and crosses the goal line, the shot will be called a "shuffle" and the play will continue." http://www.polo-velo.net/english/rules/reglesaxlesofevil.htm
I know, I know, it doesn't answer your question. It's all I could find.