Defender with one foot off the court

[OverAndBack]

We were told in the course that I took that a defender not only couldn't have one foot on the court and one on the court and establish a legit defensive position on the charge/block thing (new rule, I know that), but that also a defender couldn't even have one foot off the court and one on the court if he was guarding someone, anytime, anywhere.

At the time I said "Good luck being the first guy to call that," but yesterday, on an inbounds play (in a very small gym with not much room on the sides, but still), one of the players on the defending team lined up along the sideline with one foot on the court and the other in his bench area. I motioned for him to put his foot back on the floor.

Should I have let it go? Or waited until the inbounds and blown the violation? Is that kinda-sorta a plane violation on a throwin, since the sideline he was straddling was the sideline on which I was administering the throwin?

It didn't have any effect on anything, and no one said anything, I was just wondering, as part of my continuing education, in case it comes up again.