Not a stupid question at all... Tisha B'Av (10th day of the month "Av" in the Jewish Calendar) is the commemeration of the day that the Holy Temple was destroyed. It's a day of mourning and fasting. The idea of "tennis shoes" doesn't relate well in the world of $100 Nike and Rebock "tennis shoes." In ancient days, leather shoes were considered a luxury and "dressing up for an important occastion." The shoes refered to here are like the old keds or converse canvas shoes, cheap, with no leather. Since it's a day of mourning, you're not supposed to get "dressed up" or be conserned with how you look.
Mark
Again, thanks for being kind enough to explain it to me.
Honestly, what are we in the year 2004 doing with this old nonsense? Fasting, and praying is OK, but wearing expensive or leather shoes does not make sense.