Originally Posted by SystemicAnomaly
Try a search of the Wardlaw Directionals. This should shed light on inside shots and outside shots.
I'm very familiar with the directionals and just don't think that is the source of the term I/O. Maybe you are right, but there are plenty of scenarios where that view does not hold up and I'm pretty sure the I/O terms predates this quote below-
This system was developed in 1992 by Brown University Women’s Tennis Coach Paul Wardlaw.
I know I was hitting them well before 92 and pretty sure we already called it I/O. Interesting either way.